Power supply system, transportation device, and power transmission method

ABSTRACT

A power supply system includes first and second energy storages, a power transmission circuit, and circuitry. The circuitry configured to control the power transmission circuit to supply power from at least one of the first energy storage and the second energy storage to an electric load when a first remaining capacity value is larger than a first threshold value. The circuitry configured to control the power transmission circuit to supply power from the first energy storage or both of the first energy storage and the second energy storage to the electric load when the first remaining capacity value is smaller than the first threshold value. The circuitry configured to control the power transmission circuit to stop supplying power from the first energy storage to the electric load when the first remaining capacity value is smaller than a second threshold value which is smaller than the first threshold value.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. §119 to JapanesePatent Application No. 2015-232505, filed Nov. 28, 2015, entitled “PowerSupply System, Transportation Device, and Power Transmission Method.”The contents of this application are incorporated herein by reference intheir entirety.

BACKGROUND

1. Field

The present disclosure relates to a power supply system, atransportation device, and a power transmission method.

2. Description of the Related Art

A power supply system of this type, disclosed in InternationalPublication No. WO2013/038441, for example, is known in the related art.International Publication No. WO2013/038441 discloses a system forsupplying power to an electric motor for a vehicle by using two energystorage devices, namely, a high-capacity energy storage device(assembled battery) and a high-power energy storage device (assembledbattery).

In the disclosed system, power is supplied mainly from the high-capacityenergy storage device to the electric motor with the remaining capacityof the high-power energy storage device being kept at a reference value.When the remaining capacity (or state of charge (SOC)) of thehigh-capacity energy storage device is reduced to 0%, power is thensupplied from the high-power energy storage device to the electricmotor.

SUMMARY

According to a first aspect of the present invention, a power supplysystem includes a first energy storage device, a second energy storagedevice, a power transmission circuit unit, and a control device. Thesecond energy storage device has a higher power density and a lowerenergy density than the first energy storage device. The powertransmission circuit unit is disposed in a power transmission path amongan electric load, the first energy storage device, and the second energystorage device. The electric load is activated upon being supplied withpower from at least one of the first energy storage device and thesecond energy storage device. The power transmission circuit unit isconfigured to be capable of controlling power transmission among theelectric load, the first energy storage device, and the second energystorage device in accordance with a given control signal. The controldevice is configured to have a function of controlling the powertransmission circuit unit. The control device is configured to acquire afirst remaining capacity that is a remaining capacity of the firstenergy storage device. The control device is configured to control thepower transmission circuit unit to perform a control process based on afirst control rule to supply power from at least one of the first energystorage device and the second energy storage device to the electric loadwhen the first remaining capacity is larger than a predetermined firstthreshold value, to perform a control process based on a second controlrule different from the first control rule to supply power from one orboth of the first energy storage device and the second energy storagedevice to the electric load, the one or both of the first energy storagedevice and the second energy storage device including at least the firstenergy storage device, when the first remaining capacity is smaller thanthe first threshold value, and to prohibit power from being suppliedfrom at least the first energy storage device to the electric load whenthe first remaining capacity is smaller than a predetermined secondthreshold value smaller than the first threshold value.

According to a second aspect of the present invention, a powertransmission method for power transmission among an electric load, afirst energy storage device, and a second energy storage device having ahigher power density and a lower energy density than the first energystorage device in a power supply system, the power supply systemincluding the first energy storage device and the second energy storagedevice and being configured to supply power from at least one of thefirst energy storage device and the second energy storage device to theelectric load, the power transmission method includes the steps ofperforming a control process based on a first control rule to supplypower from at least one of the first energy storage device and thesecond energy storage device to the electric load when a first remainingcapacity that is a remaining capacity of the first energy storage deviceis larger than a predetermined first threshold value. A control processbased on a second control rule different from the first control rule isperformed to supply power from one or both of the first energy storagedevice and the second energy storage device to the electric load, theone or both of the first energy storage device and the second energystorage device including at least the first energy storage device, whenthe first remaining capacity is smaller than the first threshold value.Power is prohibited from being supplied from at least the first energystorage device to the electric load when the first remaining capacity issmaller than a predetermined second threshold value smaller than thefirst threshold value.

According to a third aspect of the present invention, a power supplysystem includes a first energy storage, a second energy storage, a powertransmission circuit, and circuitry. The first energy storage supplieselectric power to an electric load. The first energy storage has a firstpower density and a first energy density. The second energy storagesupplies electric power to the electric load. The second energy storagehas a second power density higher than a first power density and asecond energy density lower than the first energy density. The powertransmission circuit is connected to the electric load, the first energystorage, and the second energy storage so as to control powertransmission among the electric load, the first energy storage, and thesecond energy storage. The circuitry configured to acquire a firstremaining capacity value indicating remaining capacity of the firstenergy storage. The circuitry configured to control the powertransmission circuit to supply power from at least one of the firstenergy storage and the second energy storage to the electric load whenthe first remaining capacity value is larger than a first thresholdvalue. The circuitry configured to control the power transmissioncircuit to supply power from the first energy storage or both of thefirst energy storage and the second energy storage to the electric loadwhen the first remaining capacity value is smaller than the firstthreshold value. The circuitry configured to control the powertransmission circuit to stop supplying power from the first energystorage to the electric load when the first remaining capacity value issmaller than a second threshold value which is smaller than the firstthreshold value.

According to a fourth aspect of the present invention, a powertransmission method includes acquiring a first remaining capacity valueindicating remaining capacity of a first energy storage. Power issupplied from at least one of the first energy storage and a secondenergy storage to an electric load when the first remaining capacityvalue is larger than a first threshold value. Power is supplied from thefirst energy storage or both of the first energy storage and the secondenergy storage to the electric load when the first remaining capacityvalue is smaller than the first threshold value. Supplying power fromthe first energy storage to the electric load is stopped when the firstremaining capacity value is smaller than a second threshold value whichis smaller than the first threshold value.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings.

FIG. 1 illustrates an overall configuration of a power supply systemaccording to embodiments of the present disclosure.

FIG. 2 illustrates an example circuit configuration of a voltageconverter in the power supply system according to the embodiments.

FIG. 3 illustrates an example circuit configuration of an inverter inthe power supply system according to the embodiments.

FIG. 4 is a flowchart of a control process for a control device in thepower supply system according to the embodiments.

FIG. 5 illustrates, in map form, the relationship between a drivingforce demand and the remaining capacity of a second energy storagedevice in a normal combined-use control process in a first control mode,which is executed in executed in STEP4 in FIG. 4.

FIG. 6 is a flowchart illustrating the normal combined-use controlprocess executed in STEP4 in FIG. 4.

FIG. 7 is a flowchart illustrating the normal combined-use controlprocess executed in STEP4 in FIG. 4.

FIG. 8 is a flowchart illustrating the normal combined-use controlprocess executed in STEP4 in FIG. 4.

FIG. 9 is a flowchart illustrating the processing of STEP19 in FIG. 7 orthe processing of STEP25 in FIG. 8.

FIG. 10 is a graph illustrating the relationship between a coefficientα, which is used in the process illustrated in FIG. 9, and the remainingcapacity of the second energy storage device.

FIG. 11 illustrates, in map form, the relationship between a drivingforce demand and the remaining capacity of the second energy storagedevice in the normal combined-use control process in a second controlmode, which is executed in STEP4 in FIG. 4.

FIG. 12 illustrates, in map form, the relationship between a drivingforce demand and the remaining capacity of the second energy storagedevice in the normal combined-use control process in a third controlmode, which is executed in STEP4 in FIG. 4.

FIG. 13 is a flowchart illustrating an extended-stop control processexecuted in STEP6 in FIG. 4.

FIG. 14 is a graph illustrating an example of changes in a combinationof the respective remaining capacities of a first energy storage deviceand the second energy storage device over time.

FIG. 15 is a graph illustrating an example of changes in the remainingcapacity of the first energy storage device over time.

FIG. 16 is a graph illustrating an example of changes in the remainingcapacity of the second energy storage device over time.

FIG. 17 is a graph illustrating an example of changes in the remainingcapacity of the first energy storage device and the second energystorage device over time within a period during which the extended-stopcontrol process is executed.

FIG. 18 is a flowchart illustrating a control process for the controldevice during a regenerative operation of an electric motor (firstembodiment).

FIG. 19 illustrates a map for the process illustrated in FIG. 18.

FIG. 20 is a flowchart illustrating a control process for the controldevice during the regenerative operation of the electric motor (secondembodiment).

FIG. 21 illustrates a map for the process illustrated in FIG. 20 (orFIG. 22).

FIG. 22 is a flowchart illustrating a control process for the controldevice during the regenerative operation of the electric motor (thirdembodiment).

DESCRIPTION OF THE EMBODIMENTS

The embodiments will now be described with reference to the accompanyingdrawings, wherein like reference numerals designate corresponding oridentical elements throughout the various drawings.

First Embodiment

A first embodiment of the present disclosure will be describedhereinafter with reference to FIG. 1 to FIG. 19. Referring to FIG. 1, apower supply system 1 according to this embodiment is a system forsupplying power to an electric motor 100, which is an example of anelectric load.

In this embodiment, by way of example, the power supply system 1 ismounted in a transportation device, for example, an electrically drivenvehicle (not illustrated), that includes the electric motor 100 as apropulsion generator. The electric motor 100 is capable of performing apower-running operation for generating a driving force upon beingsupplied with power, and also performing a regenerative operation foroutputting regenerative power by using the kinetic energy of theelectrically driven vehicle (hereinafter sometimes referred to simply asvehicle).

The power supply system 1 includes a first energy storage device 2, asecond energy storage device 3, the electric motor 100, a powertransmission path 4 provided between the first energy storage device 2and the second energy storage device 3, and a control device 5 having afunction of controlling activation of the power supply system 1. Thefirst energy storage device 2 and the second energy storage device 3serve as power sources. The power supply system 1 may also includeadditional electric loads such as auxiliaries, in addition to theelectric motor 100.

The first energy storage device 2 and the second energy storage device 3are energy storage devices having different characteristics. The firstenergy storage device 2 is an energy storage device having a higherenergy density than the second energy storage device 3. The energydensity is an amount of electrical energy storable per unit weight orunit volume. Examples of the first energy storage device 2 may include alithium-ion battery, a fuel cell, and an air battery.

The second energy storage device 3 is an energy storage device having ahigher power density than the first energy storage device 2. The powerdensity is an amount of electricity that can be output per unit weightor unit volume (an amount of electrical energy per unit time or anamount of charge per unit time). Examples of the second energy storagedevice 3 may include a lithium-ion battery, a nickel-hydrogen battery,and a capacitor.

The first energy storage device 2 with a relatively high energy densityis capable of storing a greater amount of electrical energy than thesecond energy storage device 3. In addition, the first energy storagedevice 2 has a characteristic in that steady discharging withpotentially less variations in the output of the first energy storagedevice 2 prevents the progress of deterioration more than dischargingwith frequent variations in the output of the first energy storagedevice 2.

The second energy storage device 3 with a relatively higher powerdensity has a lower internal resistance (impedance) than the firstenergy storage device 2, and is thus capable of outputtinginstantaneously high power. In addition, the second energy storagedevice 3 has a characteristic in that discharging or charging with theremaining capacity being kept at an approximately intermediate valueprevents the progress of deterioration more than discharging or chargingwith the remaining capacity being biased toward the high-capacity sideor the low-capacity side. More specifically, the second energy storagedevice 3 has a characteristic in that the progress of deterioration ofthe second energy storage device 3 is more likely to occur as theremaining capacity of the second energy storage device 3 increases tothe high-capacity side or decreases to the low-capacity side from anintermediate value.

In this embodiment, the first energy storage device 2 and the secondenergy storage device 3 are each a rechargeable energy storage device.

The power transmission path 4 is constituted by a current-carrying line,a wiring pattern on a substrate, or the like. The power transmissionpath 4 has provided therein a power transmission circuit unit 11 forcontrolling power transmission among the first energy storage device 2,the second energy storage device 3, and the electric motor 100.

The power transmission path 4 includes a power transmission path 4 a foruse in power transmission between the first energy storage device 2 andthe power transmission circuit unit 11, a power transmission path 4 bfor use in power transmission between the second energy storage device 3and the power transmission circuit unit 11, and a power transmissionpath 4 c for use in power transmission between the electric motor 100and the power transmission circuit unit 11. The power transmission path4 a and 4 b are respectively provided with contactors 12 and 13 asswitch units for connection and disconnection of the power transmissionpath 4 a and 4 b.

The power transmission circuit unit 11 is configured to be capable ofcontrolling power transmission among the first energy storage device 2,the second energy storage device 3, and the electric motor 100 inaccordance with a control signal provided by the control device 5. Morespecifically, the power transmission circuit unit 11 is capable ofselectively switching between the source and target of power andcontrolling an amount of power supplied (a supplied power) from thesource of power to the target in accordance with a given control signal.

Specifically, the power transmission circuit unit 11 includes a voltageconverter 15, a voltage converter 16, and an inverter 17. The voltageconverter 15 is capable of boosting or stepping down a voltage inputfrom the first energy storage device 2 and outputting the resultingvoltage. The voltage converter 16 is capable of boosting or steppingdown a voltage input from the second energy storage device 3 andoutputting the resulting voltage. The inverter 17 is capable ofconverting direct-current (DC) power into alternating-current (AC) powerand outputting the AC power.

The voltage converters 15 and 16 are connected in parallel on the inputside of the inverter 17. The inverter 17 is further provided with acapacitor 18 on the input side thereof (the output side of the voltageconverters 15 and 16). The capacitor 18 smoothes the DC voltage to beinput to the inverter 17 (the DC voltage output from the voltageconverter 15 or 16).

The power transmission circuit unit 11 may be a circuit unit includingthe contactors 12 and 13.

The voltage converters 15 and 16 are so-called DC/DC converters, and maybe each a known one. FIG. 2 illustrates an example circuit configurationof the voltage converters 15 and 16. The voltage converter 15 or 16having the illustrated circuit configuration is a voltage convertercapable of boosting the output voltage of the corresponding one of thefirst energy storage device 2 and the second energy storage device 3 andoutputting the resulting voltage. The voltage converter 15 or 16includes a pair of primary-side terminals 21 a and 21 b connected to thecorresponding one of the first energy storage device 2 and the secondenergy storage device 3, a pair of secondary-side terminals 22 a and 22b connected to the inverter 17, a capacitor 23, a coil 24, and high-sideand low-side two switch units 27 a and 27 b. The capacitor 23, the coil24, and the switch units 27 a and 27 b are connected between the pair ofprimary-side terminals 21 a and 21 b and the pair of secondary-sideterminals 22 a and 22 b in an illustrated way. Each of the switch units27 a and 27 b includes a semiconductor switch element 25, such as atransistor, and a diode 26, which are connected in parallel.

The voltage converter 15 or 16 having the configuration described aboveis capable of controlling the respective semiconductor switch elements25 of the switch units 27 a and 27 b to be turned on or off inaccordance with a control signal having a predetermined duty ratio(so-called duty signal) to output from the secondary-side terminals 22 aand 22 b a DC voltage obtained by boosting a DC voltage input to theprimary-side terminals 21 a and 21 b at a required boosting ratio or tooutput a DC voltage, which is obtained by stepping down a DC voltageinput to the secondary-side terminals 22 a and 22 b at a requiredstep-down ratio, from the primary-side terminals 21 a and 21 b. Theboosting ratio or the step-down ratio is variably controllable.

The voltage converter 15 or 16 is further capable of controlling therespective semiconductor switch elements 25 of the switch units 27 a and27 b to be turned off to interrupt current flow (power transmission)from the secondary side to the primary side.

As a supplementary explanation, the voltage converters 15 and 16 mayhave a circuit configuration other than that illustrated in FIG. 2.Furthermore, any one or both of the voltage converters 15 and 16 may beconfigured to step down a voltage input from the first energy storagedevice 2 or the second energy storage device 3 and to output theresulting voltage. One of the voltage converters 15 and 16 may beomitted. The necessity of the voltage converter 15 or 16 or the voltageconversion type of the voltage converter 15 or 16 (namely, boosting orstepping down) may be selected from a variety of combinations inaccordance with the voltage necessary to activate the electric load, therespective output voltages of the first energy storage device 2 and thesecond energy storage device 3, and so on.

For example, the first energy storage device 2 is a higher-voltageenergy storage device than the second energy storage device 3. In thiscase, if one of the voltage converters 15 and 16 is to be omitted, it ismore preferable that the voltage converter 15, which is connected to thefirst energy storage device 2, be omitted. Omission of one of thevoltage converters 15 and 16 can reduce the cost required to realize apower supply system.

The inverter 17 may be an inverter having a known circuit configuration.FIG. 3 illustrates an example circuit configuration of the inverter 17when the electric motor 100 is a three-phase electric motor, forexample. The inverter 17 illustrated in FIG. 3 is configured such thatthree-phase arms 32 u, 32 v, and 32 w of the U, V, and W phases areconnected in parallel between a pair of power supply terminals 31 a and31 b to which a DC voltage is applied. Each of the arms 32 u, 32 v, and32 w of the respective phases includes high-side and low-side two switchunits 35 a and 35 b that are connected in series. Each of the switchunits 35 a and 35 b includes a diode 34 and a semiconductor switchelement 33 such as a transistor that are connected in parallel. Themidpoints of the switch units 35 a and 35 b of the arms 32 u, 32 v, and32 w of the respective phases serve as three-phase AC power outputunits.

The inverter 17 having the configuration described above is capable ofcontrolling the respective semiconductor switch elements 33 of theswitch units 35 a and 35 b of the arms 32 u, 32 v, and 32 w of therespective phases to be turned on or off in accordance with a controlsignal generated by using the pulse width modulation (PWM) controlmethod or the like to convert a DC power input to the power supplyterminals 31 a and 31 b into three-phase AC power, and outputting the ACpower to the electric motor 100 (the electric motor 100 which is inpower-running operation).

During the regenerative operation of the electric motor 100 (duringgeneration of power), the inverter 17 is capable of controlling therespective semiconductor switch elements 33 of the switch units 35 a and35 b of the arms 32 u, 32 v, and 32 w of the respective phases to beturned on or off in accordance with a control signal having apredetermined duty ratio (so-called duty signal) to convert athree-phase AC power input from the electric motor 100 into DC power,and outputting the DC power from the power supply terminals 31 a and 31b.

As a supplementary explanation, the number of phases (the number ofarms) of the inverter 17 is set in accordance with the number of phasesof the AC power necessary to activate the electric load. Furthermore, ifthe electric load is an electric load (e.g., a DC motor) activated bycausing DC power to flow therethrough, the inverter 17 may be omitted.

The power transmission circuit unit 11 having the configurationdescribed above is configured to control the voltage converters 15 and16 and the inverter 17 (specifically, provide each of the voltageconverters 15 and 16 and the inverter 17 with a control signal (dutysignal having a predetermined duty ratio) for turning on or off thesemiconductor switch elements 25 or 33) to control power transmissionamong the first energy storage device 2, the second energy storagedevice 3, and the electric motor 100.

For example, the following operation may be performed during thepower-running operation of the electric motor 100: supplying power fromone or both of the first energy storage device 2 and the second energystorage device 3 to the electric motor 100, supplying power from thefirst energy storage device 2 to the second energy storage device 3 tocharge the second energy storage device 3, or supplying regenerativepower which is obtained during the regenerative operation of theelectric motor 100 to charge one or both of the first energy storagedevice 2 and the second energy storage device 3.

In this embodiment, the first energy storage device 2 is not chargedwith power supplied by the second energy storage device 3. However, thepower transmission circuit unit 11 may be controlled so that the firstenergy storage device 2 is charged with power supplied by the secondenergy storage device 3.

The control device 5 is constituted by an electronic circuit unitincluding a central processing unit (CPU), a random access memory (RAM),a read-only memory (ROM), an interface circuit, and so on. The controldevice 5 may be constituted by a plurality of electronic circuit unitsthat are capable of communicating with each other.

The control device 5 includes a power transmission controller 41 and aremaining capacity detector 42 as functions implemented by a hardwareconfiguration to be mounted therein or a program (softwareconfiguration) installed therein. The power transmission controller 41controls the power transmission circuit unit 11 to control powertransmission among the first energy storage device 2, the second energystorage device 3, and the electric motor 100. The remaining capacitydetector 42 detects the respective remaining capacities (called statesof charge (SOCs)) of the first energy storage device 2 and the secondenergy storage device 3.

The control device 5 receives, as information necessary to implement thefunctions described above, a driving/braking force demand, a controlmode, and various kinds of sensing data. The driving/braking forcedemand is constituted by a driving force demand that is a request valuefor a driving force (driving torque) to be generated by the electricmotor 100 during the power-running operation or a braking force demandthat is a request value for a braking force (regenerative torque) to begenerated by the electric motor 100 during the regenerative operation.The control mode specifies how the power transmission circuit unit 11 iscontrolled.

The driving/braking force demand is set by a vehicle control device (notillustrated) while an electrically driven vehicle in which the powersupply system 1 according to this embodiment is mounted is traveling, inaccordance with values such as the respective detected values of theamount of operation of the accelerator pedal and the amount of operationof the brake pedal.

The control device 5 may have a function of setting a driving/brakingforce demand.

The control mode is set by, for example, the driver of the electricallydriven vehicle by operating a mode switching operation device (notillustrated). In this embodiment, three control modes, namely, first tothird control modes described below, are selectively set for the controldevice 5. The control mode may be automatically set in accordance withthe state of travel of the electrically driven vehicle, the environmentin which the electrically driven vehicle is traveling, or the like.

As to the sensing data, for example, the following data is input to thecontrol device 5: the detection data of a current sensor 51, a voltagesensor 52, a temperature sensor 53, a current sensor 54, a voltagesensor 55, a temperature sensor 56, a current sensor 57, a voltagesensor 58, a current sensor 59, a current sensor 60, a voltage sensor61, a current sensor 62, and a voltage sensor 63. The current sensor 51detects a current flowing through the first energy storage device 2. Thevoltage sensor 52 detects an output voltage of the first energy storagedevice 2. The temperature sensor 53 detects a temperature of the firstenergy storage device 2. The current sensor 54 detects a current flowingthrough the second energy storage device 3. The voltage sensor 55detects an output voltage of the second energy storage device 3. Thetemperature sensor 56 detects a temperature of the second energy storagedevice 3. The current sensor 57 and the voltage sensor 58 detect acurrent and voltage on the input side of the voltage converter 15 (thefirst energy storage device 2 side), respectively. The current sensor 59detects a current on the output side of the voltage converter 15 (theinverter 17 side). The current sensor 60 and the voltage sensor 61detect a current and voltage on the input side of the voltage converter16 (the second energy storage device 3 side), respectively. The currentsensor 62 detects a current on the output side of the voltage converter16 (the inverter 17 side). The voltage sensor 63 detects a voltage onthe input side of the inverter 17 (the voltages on the respective outputsides of the voltage converters 15 and 16). The above-described piecesof detection data are input to the control device 5.

The remaining capacity detector 42 of the control device 5 sequentiallydetects (estimates) the remaining capacity of the first energy storagedevice 2 by using the detection data of the sensors for the first energystorage device 2, namely, the current sensor 51, the voltage sensor 52,and the temperature sensor 53, for example. Further, the remainingcapacity detector 42 sequentially detects (estimates) the remainingcapacity of the second energy storage device 3 by using the detectiondata of the sensors for the second energy storage device 3, namely, thecurrent sensor 54, the voltage sensor 55, and the temperature sensor 56,for example.

There have hitherto been proposed a variety of techniques for detectingthe remaining capacity of an energy storage device. A known techniquemay be employed as a technique for detecting the remaining capacities ofthe first energy storage device 2 and the second energy storage device3.

The technique for detecting the respective remaining capacities of thefirst energy storage device 2 and the second energy storage device 3 maybe a technique that does not use the detection data of any one of thecurrent flow, the output voltage, and the temperature, or a techniquethat uses any other detection data. A detection device different fromthe control device 5 may perform a process of detecting the respectiveremaining capacities of the first energy storage device 2 and the secondenergy storage device 3.

The power transmission circuit unit 11 controls the voltage converters15 and 16 and the inverter 17 of the power transmission circuit unit 11by, for example, appropriately using the detection data of the currentsensors 57, 59, 60, and 62 and the voltage sensors 58, 61, and 63, thedriving/braking force demand of the electric motor 100, and the detectedvalues of the respective remaining capacities of the first energystorage device 2 and the second energy storage device 3, which areobtained by the remaining capacity detector 42.

Control Process for Power Transmission Controller

A control process for the power transmission controller 41 of thecontrol device 5 will now be described in detail hereinafter.

During the travel of the vehicle, the control device 5 sequentiallyexecutes a control process illustrated in a flowchart in FIG. 4 by usingthe power transmission controller 41 at intervals of a predeterminedcontrol process period. The control process illustrated in the flowchartin FIG. 4 is a control process performed during the power-runningoperation of the electric motor 100.

In STEP1, the power transmission controller 41 acquires the currentlyset control mode. Then, in STEP2, the power transmission controller 41acquires, from the remaining capacity detector 42, a detected value ofthe remaining capacity SOC1 of the first energy storage device 2(hereinafter sometimes referred to as first remaining capacity SOC1) anda detected value of the remaining capacity SOC2 of the second energystorage device 3 (hereinafter sometimes referred to as second remainingcapacity SOC2).

Then, in STEP3, the power transmission controller 41 determines whetheror not the following conditions hold true: the detected value of thefirst remaining capacity SOC1 is greater than or equal to apredetermined threshold value B1_th1 and the detected value of thesecond remaining capacity SOC2 is greater than or equal to apredetermined lower limit value B2_min.

The threshold value B1_th1 for the first remaining capacity SOC1 is athreshold value determined in advance as a limit value of the firstremaining capacity SOC1 which is required for a normal combined-usecontrol process described below. The threshold value B1_th1 may be, forexample, a limit remaining capacity value that allows only the firstenergy storage device 2 to supply a supplied power required for theelectric motor 100 to generate a certain output (e.g., a supplied powerrequired for the vehicle to cruise at a predetermined vehicle speed) tothe electric motor 100. The threshold value B1_th1 is set to a valueslightly higher than a lower limit value B1_min (a near-zero value). Thelower limit value B1_min is a limit remaining capacity value that allowsthe first energy storage device 2 to supply power to outside so as toprevent the first energy storage device 2 from deteriorating.

The lower limit value B2_min for the second remaining capacity SOC2 is alimit remaining capacity value (a near-zero value) that allows thesecond energy storage device 3 to supply power to outside so as toprevent the second energy storage device 3 from deteriorating.

The determination result of STEP3 is affirmative when the firstremaining capacity SOC1 and the second remaining capacity SOC2 takevalues that fall in a normal range (common range). In this situation, inSTEP4, the power transmission controller 41 executes a normalcombined-use control process corresponding to the currently set controlmode. The normal combined-use control process is a process forcontrolling the power transmission circuit unit 11 to supply power fromone or both of the first energy storage device 2 and the second energystorage device 3 to the electric motor 100 in the manner correspondingto the control mode and to, when power is supplied from the first energystorage device 2 to the electric motor 100, supply power from the firstenergy storage device 2 to charge the second energy storage device 3, ifnecessary. The details of the normal combined-use control process willbe described below.

The normal combined-use control process allows the second energy storagedevice 3 to be charged with power supplied from the first energy storagedevice 2, if necessary, whereas the remaining capacity SOC1 of the firstenergy storage device 2 decreases. Thus, the first remaining capacitySOC1 becomes smaller than the threshold value B1_th1 and thedetermination result of STEP3 becomes negative.

When the determination result of STEP3 is negative, then, in STEP5, thepower transmission controller 41 determines whether or not the followingconditions hold true: the detected value of the first remaining capacitySOC1 is greater than or equal to the lower limit value B1_min and thedetected value of the second remaining capacity SOC2 is greater than orequal to the lower limit value B2_min.

The determination result of STEP5 is affirmative when, in particular,the remaining capacity of the first energy storage device 2 is low butit is possible to supply power to the electric motor 100 for a certaintime period by the cooperation of the first energy storage device 2 andthe second energy storage device 3 so as to allow the electric motor 100to generate a demanded driving force.

In this situation, in STEP6, the power transmission controller 41executes an extended-stop control process. The extended-stop controlprocess is a process for controlling the power transmission circuit unit11 so that the remaining capacity of both the first energy storagedevice 2 and the second energy storage device 3 is consumed as much aspossible. The details of the extended-stop control process will bedescribed below.

The determination result of STEP5 is negative when it is difficult tosupply power from the first energy storage device 2 and the secondenergy storage device 3 to the electric motor 100. In this situation,the power transmission controller 41 executes a stop process. In thestop process, the power transmission controller 41 controls the voltageconverters 15 and 16 or the contactors 12 and 13 to interrupt the outputof the first energy storage device 2 and the second energy storagedevice 3 (discharging to the load side) and to hold the interruptionstate.

In the stop process, the control device 5 generates an alarm output(visual output or audio output) to alert the vehicle driver that, forexample, the vehicle is no longer able to travel or the electric motor100 is no longer able to operate due to the insufficient remainingcapacity of the first energy storage device 2 and the second energystorage device 3.

Normal Combined-Use Control Process

The normal combined-use control process in STEP4 described above willnow be described in detail. Brief definitions of terms as used in thefollowing description are presented below.

In the following description, the “output” or “input” of each of thefirst energy storage device 2 and the second energy storage device 3,the “supplied power” or the “charging power” refers to an amount ofelectricity expressed as a value of (electric) power (an amount ofelectrical energy per unit time), for example.

The “supplied power corresponding to a driving force demand DT_dmd” ofthe electric motor 100 refers to an amount of power to be supplied whichallows a driving force generated by the electric motor 100 when thispower is supplied to the electric motor 100 to be identical to orsubstantially identical to the driving force demand DT_dmd.

The “supplied power corresponding to the driving force demand DT_dmd” isbased on the driving force demand DT_dmd and the rotational speed of theelectric motor 100 (specifically, the rotational speed of a rotor or anoutput shaft of the electric motor 100) when the “supplied power” refersto an amount of electricity expressed as a value of (electric) power. Inthis case, the value of the “supplied power corresponding to the drivingforce demand DT_dmd” can be determined by using, for example, thedriving force demand DT_dmd and the detected value of the rotationalspeed of the electric motor 100 in accordance with a map or anoperational expression.

The “supplied power corresponding to a certain threshold value” relatedto the driving force demand DT_dmd refers to an amount of power to besupplied which corresponds to the driving force demand DT_dmd when thedriving force demand DT_dmd is made to coincide with the thresholdvalue.

First Control Mode

Based on the terms defined above, a case in which the control mode isset to the first control mode, which is a basic control mode among thefirst to third control modes, will be described with reference to FIG. 5to FIG. 10.

The first control mode is a control mode for controlling the powertransmission circuit unit 11 so as to prevent as much as possible theprogress of deterioration of the first energy storage device 2 and thesecond energy storage device 3.

An overview of the normal combined-use control process in the firstcontrol mode will be described with reference to FIG. 5. FIG. 5illustrates, in map form, the relationship in the first control modebetween the second remaining capacity SOC2 and the proportion of powersto be output by the first energy storage device 2 and the second energystorage device 3 with respect to the amount of electricity to besupplied (the supplied power) to the electric motor 100 in accordancewith the driving force demand DT_dmd of the electric motor 100.

In FIG. 5, diagonally hatched areas represent areas in which the firstenergy storage device 2 is responsible for supplying part or all of thesupplied power to the electric motor 100, and shaded areas representareas in which the second energy storage device 3 is responsible forsupplying part or all of the supplied power to the electric motor 100.

More specifically, a diagonally hatched area adjoining the line(horizontal axis) along which the driving force demand DT_dmd=0 holdsrepresents an area within which only the first energy storage device 2is responsible for supplying all of the supplied power to the electricmotor 100, and a shaded area adjoining the line (horizontal axis)represents an area within which only the second energy storage device 3is responsible for supplying all of the supplied power to the electricmotor 100.

A shaded area above the diagonally hatched areas or a diagonally hatchedarea above the shaded areas represents an area within which both thefirst energy storage device 2 and the second energy storage device 3 areresponsible for supplying the supplied power to the electric motor 100.

In the normal combined-use control process in the first control mode, asillustrated in FIG. 5, the proportion of powers to be output by thefirst energy storage device 2 and the second energy storage device 3 inaccordance with the driving force demand DT_dmd of the electric motor100 is different depending on when the value of the second remainingcapacity SOC2 falls within a high-remaining-capacity area that satisfiesSOC2≧B2_th1 (including the remaining capacity value reaching fullstate-of-charge (100%)), when the value of the second remaining capacitySOC2 falls within a medium-remaining-capacity area that satisfiesB2_th1>SOC2≧B2_th2, or when the value of the second remaining capacitySOC2 falls within a low-remaining-capacity area that satisfiesB2_th2>SOC2. The supplied power corresponding to the driving forcedemand DT_dmd of the electric motor 100 is fed from one or both of thefirst energy storage device 2 and the second energy storage device 3 tothe electric motor 100 in the proportion for the high-, medium-, orlow-remaining-capacity area.

In this embodiment, more specifically, the low-remaining-capacity areais a remaining capacity area that satisfies B2_th2>SOC2≧B2_min since thenormal combined-use control process is a process performed when thedetected value of the second remaining capacity SOC2 is greater than orequal to the lower limit value B2_min.

In FIG. 5, the threshold values B2_th1 and B2_th2, which are used toseparate the second remaining capacity SOC2, are threshold values (fixedvalues) determined in advance as those for the first control mode. Thethreshold values B2_th1 and B2_th2 are set in advance based on anexperiment or the like so that the medium-remaining-capacity area whoseboundaries are defined by the threshold values B2_th1 and B2_th2 is aremaining capacity area within which the actual value of the secondremaining capacity SOC2 preferably falls to prevent as much as possiblethe progress of deterioration of the second energy storage device 3.Accordingly, the medium-remaining-capacity area whose boundaries aredefined by the threshold values B2_th1 and B2_th2 is a remainingcapacity area that can prevent the progress of deterioration of thesecond energy storage device 3, as desired, when the second energystorage device 3 is charged or discharged in such a manner that theactual value of the second remaining capacity SOC2 is kept within themedium-remaining-capacity area as much as possible.

The normal combined-use control process in the first control mode willnow be described in a more specific manner.

In the normal combined-use control process, the power transmissioncontroller 41 sequentially executes a process illustrated in a flowchartin FIG. 6 to FIG. 8 at intervals of a predetermined control processperiod.

In STEP11, the power transmission controller 41 acquires the drivingforce demand DT_dmd of the electric motor 100. Then, in STEP12, thepower transmission controller 41 determines whether or not the detectedvalue of the second remaining capacity SOC2, which is acquired in STEP2,is greater than or equal to the threshold value B2_th1, which is thelower limit of the high-remaining-capacity area.

The determination result of STEP12 is affirmative when the detectedvalue of the second remaining capacity SOC2 falls within thehigh-remaining-capacity area. In this case, then, in STEP13, the powertransmission controller 41 determines whether or not the driving forcedemand DT_dmd is larger than a predetermined threshold value DT_th1.

In an example of this embodiment, the threshold value DT_th1 is apredetermined constant value (fixed value) that has been determined inadvance. The threshold value DT_th1 may be, for example, an upper limitdriving force value, or a nearby driving force value, that can begenerated by the electric motor 100 using power supplied only from thesecond energy storage device 3 when the second remaining capacity SOC2falls within the high-remaining-capacity area. The threshold valueDT_th1 may be set to be variable by using, for example, the detectedvalue of the temperature of the second energy storage device 3, which isobtained by the temperature sensor 56, in order to more appropriatelyprevent deterioration of the second energy storage device 3.

The determination result of STEP13 is affirmative within the diagonallyhatched area in the high-remaining-capacity area illustrated in FIG. 5.In this case, in STEP14, the power transmission controller 41 controlsthe power transmission circuit unit 11 so that an output P2 of thesecond energy storage device 3 coincides with a supplied powercorresponding to the threshold value DT_th1 and so that an output P1 ofthe first energy storage device 2 coincides with the power deficitobtained by subtracting the output P2, which is a portion that thesecond energy storage device 3 is responsible for supplying, from thesupplied power corresponding to the driving force demand DT_dmd.

The output P1 of the first energy storage device 2 is, specifically, anamount of electricity output from (an amount of power discharged from)the first energy storage device 2, and the output P2 of the secondenergy storage device 3 is, specifically, an amount of electricityoutput from (an amount of power discharged from) the first energystorage device 2.

Accordingly, the supplied power corresponding to the driving forcedemand DT_dmd is fed from both the first energy storage device 2 and thesecond energy storage device 3 to the electric motor 100 in such amanner that the sum of the output P1 of the first energy storage device2 and the output P2 of the second energy storage device 3 coincides withthe supplied power corresponding to the driving force demand DT_dmd. Inthis case, a portion (the output P2), which the second energy storagedevice 3 is responsible for supplying, of the supplied powercorresponding to the driving force demand DT_dmd is equal to thesupplied power corresponding to the threshold value DT_th1.

The processing of STEP14 can be, specifically, executed in the followingway, for example. A target value for the input voltage for controllingthe inverter 17 (=the output voltages of the voltage converters 15 and16) is set in accordance with the detected value of the rotational speedof the electric motor 100 or the like. In addition, the supplied powercorresponding to the threshold value DT_th1 is set as the target valuefor the output power of the voltage converter 16, and a supplied powerobtained by subtracting the output P2 (=the supplied power correspondingto the threshold value DT_th1), which is a portion that the secondenergy storage device 3 is responsible for supplying, from the suppliedpower corresponding to the driving force demand DT_dmd is set as thetarget value for the output power of the voltage converter 15.

Further, the voltage converters 15 and 16 are controlled by using acontrol signal (duty signal) so as to realize the target value for theinput voltage of the inverter 17 and the target values for therespective output powers of the voltage converters 15 and 16. Also, theinverter 17 is feedback-controlled by using a control signal (dutysignal) so as to cause a target current to flow through the electricmotor 100. The target current is a current that can realize a targetpower set in accordance with the driving force demand DT_dmd or a targetpower obtained by limiting the target power through a limiting process(a limiting process for limiting the respective outputs of the energystorage devices 2 and 3).

On the other hand, the determination result of STEP13 is negative withinthe shaded area in the high-remaining-capacity area illustrated in FIG.5. In this case, in STEP15, the power transmission controller 41controls the power transmission circuit unit 11 so that the output P2 ofthe second energy storage device 3 coincides with the supplied powercorresponding to the driving force demand DT_dmd.

Accordingly, the supplied power corresponding to the driving forcedemand DT_dmd is fed to the electric motor 100 only from the secondenergy storage device 3 without using the first energy storage device 2.

The processing of STEP15 can be, specifically, executed in the followingway, for example. A target value for the input voltage of the inverter17 (=the output voltage of the voltage converter 16) is set inaccordance with the detected value of the rotational speed of theelectric motor 100 or the like. In addition, the supplied powercorresponding to the driving force demand DT_dmd is set as the targetvalue for the output power of the voltage converter 16.

Further, the voltage converter 16 is controlled so as to realize thetarget value for the input voltage of the inverter 17 and the targetvalue for the output power of the voltage converter 16. Also, theinverter 17 is feedback-controlled so as to cause the target currentcorresponding to the driving force demand DT_dmd to flow through theelectric motor 100.

Further, the voltage converter 15 is controlled to be in power supplyinterruption state. Alternatively, the contactor 12 on the first energystorage device 2 side is controlled to be turned off.

As described above, when the detected value of the second remainingcapacity SOC2 falls within the high-remaining-capacity area, power issupplied to the electric motor 100 from an energy storage deviceincluding at least the second energy storage device 3 out of the firstenergy storage device 2 and the second energy storage device 3 duringthe power-running operation of the electric motor 100. This allows thesecond energy storage device 3 to be actively discharged to make theremaining capacity SOC2 of the second energy storage device 3 approachthe medium-remaining-capacity area. Thus, the second energy storagedevice 3 can be prevented from deteriorating while the driving forcedemand DT_dmd of the electric motor 100 is met.

As a supplementary explanation, the threshold value DT_th1, which isused in the determination processing of STEP13, may be set in a waydifferent from that described above. For example, the threshold valueDT_th1 may be set so that the supplied power corresponding to thethreshold value DT_th1 is equal to a predetermined constant value (e.g.,an upper-limit supplied power that can be output by the second energystorage device 3 within the high-remaining-capacity area or a nearbyconstant value of supplied power). The threshold value DT_th1 may alsobe set to vary depending on the detected value of the second remainingcapacity SOC2.

When the determination result of STEP12 is negative, in STEP16, thepower transmission controller 41 further determines whether or not thedetected value of the second remaining capacity SOC2 is greater than orequal to the threshold value B2_th2, which is the lower limit of themedium-remaining-capacity area.

The determination result of STEP16 is affirmative when the detectedvalue of the second remaining capacity SOC2 falls within themedium-remaining-capacity area. In this situation, then, in STEP17 (seeFIG. 7), the power transmission controller 41 determines whether or notthe driving force demand DT_dmd is larger than a predetermined thresholdvalue DT_th2.

In an example of this embodiment, for example, as illustrated in FIG. 5,the predetermined threshold value DT_th2 is a threshold value set to bevariable in accordance with the detected value of the second remainingcapacity SOC2. Specifically, the threshold value DT_th2 is set toincrease as the detected value of the second remaining capacity SOC2decreases. In addition, the threshold value DT_th2 is set to a drivingforce value larger than the driving force that can be generated by theelectric motor 100 when a base supplied power P1_base described below isfed to the electric motor 100.

The determination result of STEP17 is affirmative within the diagonallyhatched area above the shaded area in the medium-remaining-capacity areaillustrated in FIG. 5. In this case, in STEP18, the power transmissioncontroller 41 controls the power transmission circuit unit 11 so thatthe output P2 of the second energy storage device 3 coincides with apredetermined value of supplied power and so that the output P1 of thefirst energy storage device 2 coincides with the power deficit obtainedby subtracting the output P2, which is a portion that the second energystorage device 3 is responsible for supplying, from the supplied powercorresponding to the driving force demand DT_dmd.

In this case, specific control of the power transmission circuit unit 11can be performed in a manner similar to that in STEP14 in FIG. 6.

Accordingly, the supplied power corresponding to the driving forcedemand DT_dmd is fed from both the first energy storage device 2 and thesecond energy storage device 3 to the electric motor 100 in such amanner that the sum of the output P1 of the first energy storage device2 and the output P2 of the second energy storage device 3 coincides withthe supplied power corresponding to the driving force demand DT_dmd. Inthis case, a portion of the supplied power corresponding to the drivingforce demand DT_dmd which the second energy storage device 3 isresponsible for supplying is equal to a predetermined value of suppliedpower.

In this case, the predetermined value of supplied power, which is outputfrom the second energy storage device 3, may be, for example, anupper-limit supplied power that can be output by the second energystorage device 3 within the medium-remaining-capacity area or a nearbyconstant value of supplied power. Alternatively, the predetermined valueof supplied power may be, for example, a supplied power set to varydepending on the detected value of the second remaining capacity SOC2.

On the other hand, when the determination result of STEP17 is negative,then, in STEP19, the power transmission controller 41 determines thebase supplied power P1_base, which is a “base” value of the output P1 ofthe first energy storage device 2, in accordance with the detected valueof the second remaining capacity SOC2.

The base supplied power P1_base is a lower limit amount of electricityto be output from the first energy storage device 2 regardless of thedriving force demand DT_dmd when the detected value of the secondremaining capacity SOC2 falls within the medium-remaining-capacity areaor the low-remaining-capacity area. That is, in this embodiment, thepower transmission circuit unit 11 is controlled so that the basesupplied power P1_base or a larger supplied power is output from thefirst energy storage device 2 regardless of the driving force demandDT_dmd when the detected value of the second remaining capacity SOC2falls within the medium-remaining-capacity area or thelow-remaining-capacity area.

The base supplied power P1_base is set in a way illustrated in aflowchart in FIG. 9, for example. Specifically, in STEP31, the powertransmission controller 41 determines a coefficient α in accordance withthe detected value of the second remaining capacity SOC2. Thecoefficient α specifies a pattern in which the base supplied powerP1_base changes in accordance with the detected value of the secondremaining capacity SOC2.

The coefficient α is set from the detected value of the second remainingcapacity SOC2 in accordance with, for example, a pattern depicted on agraph in FIG. 10 by using a map created in advance or by using anoperational expression. In the illustrated example, the coefficient αtakes a value in the range from “0” to “1”. The value of the coefficientα is basically set to increase as the detected value of the secondremaining capacity SOC2 decreases within a remaining capacity area(low-side remaining capacity area) obtained by combining themedium-remaining-capacity area and the low-remaining-capacity area ofthe second energy storage device 3.

More specifically, when the detected value of the second remainingcapacity SOC2 falls within the medium-remaining-capacity area, the valueof the coefficient α is set to successively increase from “0” to “1” asthe detected value of the second remaining capacity SOC2 decreases fromthe threshold value B2_th1, which is the upper limit of themedium-remaining-capacity area, to the threshold value B2_th2, which isthe lower limit of the medium-remaining-capacity area.

When the detected value of the second remaining capacity SOC2 fallswithin the low-remaining-capacity area, the value of the coefficient αis set to the maximum value “1”.

Then, in STEP32, the power transmission controller 41 multiplies asupplied power P1 b having a predetermined (fixed) value by the value ofthe coefficient α determined in the way described above to calculate thebase supplied power P1_base (=α×P1 b). The supplied power P1 b is amaximum value of the base supplied power P1_base.

Accordingly, the base supplied power P1_base is determined to change inthe same or substantially the same pattern as that of the coefficient αin accordance with the detected value of the second remaining capacitySOC2.

The base supplied power P1_base may be defined by, for example, settingan upper limit of the output P1 of the first energy storage device 2 inaccordance with the detected value of the first remaining capacity SOC1or the like and, when the base supplied power P1_base calculated in theway described above exceeds the upper limit, executing a limitingprocess after the processing of STEP32 to forcibly limit the basesupplied power P1_base to the upper limit.

Alternatively, for example, the base supplied power P1_base may bedetermined, instead of by performing the processing of STEP31 and STEP32, directly from the detected value of the second remaining capacitySOC2 by using a map created in advance or by using an operationalexpression.

Referring back to FIG. 7, after the processing of STEP19 has beenexecuted in the way described above, then, in STEP20, the powertransmission controller 41 determines whether or not the supplied powercorresponding to the driving force demand DT_dmd is less than or equalto the base supplied power P1_base. The determination processing inSTEP20 is equivalent to a process of determining whether or not thedriving force demand DT_dmd is less than or equal to a threshold valueobtained by converting the base supplied power P1_base into a drivingforce value in accordance with the detected value of the rotationalspeed of the electric motor 100. This threshold value is a thresholdvalue DT_th4 indicated by a broken line in FIG. 5. The threshold valueDT_th4 indicated by the broken line in FIG. 5 is a threshold valueobtained when the rotational speed of the electric motor 100 is set tobe constant.

The determination result of STEP20 is affirmative within the bottomdiagonally hatched area in the medium-remaining-capacity areaillustrated in FIG. 5. In this situation, in STEP21, the powertransmission controller 41 controls the power transmission circuit unit11 so that the output P1 of the first energy storage device 2 coincideswith the base supplied power P1_base and so that the input of the secondenergy storage device 3, that is, the charging power, coincides with asupplied power corresponding to the surplus power obtained bysubtracting the supplied power corresponding to the driving force demandDT_dmd from the base supplied power P1_base (the surplus suppliedpower).

Accordingly, the base supplied power P1_base, which is set in the waydescribed above in accordance with the detected value of the secondremaining capacity SOC2, is output from the first energy storage device2 regardless of the driving force demand DT_dmd. In addition, a suppliedpower corresponding to the driving force demand DT_dmd within the basesupplied power P1_base is fed from the first energy storage device 2 tothe electric motor 100 and the surplus supplied power obtained bysubtracting the supplied power corresponding to the driving force demandDT_dmd from the base supplied power P1_base is supplied from the firstenergy storage device 2 to charge the second energy storage device 3.

The processing of STEP21 can be, specifically, executed in the followingway, for example. A target value for the input voltage of the inverter17 (=the output voltage of the voltage converter 15) is set inaccordance with the detected value of the rotational speed of theelectric motor 100 or the like. In addition, the base supplied powerP1_base is set as the target value for the output power of the voltageconverter 15, and a supplied power obtained by subtracting the suppliedpower corresponding to the driving force demand DT_dmd from the basesupplied power P1_base is set as the target value for the power to besupplied from the input side of the voltage converter 16 (the secondenergy storage device 3 side) to the second energy storage device 3.

Further, the voltage converter 15 is controlled so as to realize thetarget value for the input voltage of the inverter 17 and the targetvalue for the output power of the voltage converter 15, and the voltageconverter 16 is controlled so as to realize the target value for thepower to be supplied from the voltage converter 16 to the second energystorage device 3. Also, the inverter 17 is feedback-controlled so as tocause the target current corresponding to the driving force demandDT_dmd to flow through the electric motor 100.

When the base supplied power P1_base coincides with the supplied powercorresponding to the driving force demand DT_dmd, the input (thecharging power) of the second energy storage device 3 is zero. Thus, thevoltage converter 16 is controlled to be in power supply interruptionstate or the contactor 13 on the second energy storage device 3 side iscontrolled to be turned off.

On the other hand, the determination result of STEP20 is negative withinthe shaded area in the medium-remaining-capacity area illustrated inFIG. 5. In this case, in STEP22, the power transmission controller 41controls the power transmission circuit unit 11 so that the output P1 ofthe first energy storage device 2 coincides with the base supplied powerP1_base and so that the output P2 of the second energy storage device 3coincides with the power deficit obtained by subtracting the basesupplied power P1_base from the supplied power corresponding to thedriving force demand DT_dmd.

In this case, specific control of the power transmission circuit unit 11can be performed in a manner similar to that in STEP14 in FIG. 6.

Accordingly, the supplied power corresponding to the driving forcedemand DT_dmd is fed from both the first energy storage device 2 and thesecond energy storage device 3 to the electric motor 100 in such amanner that the sum of the output P1 of the first energy storage device2 and the output P2 of the second energy storage device 3 coincides withthe supplied power corresponding to the driving force demand DT_dmd. Inthis case, a portion (the output P1) of the supplied power correspondingto the driving force demand DT_dmd which the first energy storage device2 is responsible for supplying is equal to the base supplied powerP1_base, which is set in the way described above in accordance with thedetected value of the second remaining capacity SOC2.

As a supplementary explanation, when, in STEP22, the output P2 of thesecond energy storage device 3 (the power deficit obtained bysubtracting the base supplied power P1_base from the supplied powercorresponding to the driving force demand DT_dmd) exceeds theupper-limit supplied power that can be output by the second energystorage device 3 within the medium-remaining-capacity area, the outputP2 of the second energy storage device 3 may be limited to theupper-limit supplied power and the power transmission circuit unit 11may be controlled by using processing similar to that of STEP18.

Alternatively, the threshold value DT_th2 in the determinationprocessing in STEP17 may be set so that a supplied power correspondingto the threshold value DT_th2 coincides with a value obtained by addingthe upper-limit supplied power that can be output by the second energystorage device 3, or a nearby constant value of supplied power, to thebase supplied power P1_base.

As described above, when the detected value of the second remainingcapacity SOC2 falls within the medium-remaining-capacity area, power issupplied to the electric motor 100 from an energy storage deviceincluding at least the first energy storage device 2 out of the firstenergy storage device 2 and the second energy storage device 3 duringthe power-running operation of the electric motor 100.

In addition, when the driving force demand DT_dmd is less than or equalto the threshold value DT_th2, the output P1 of the first energy storagedevice 2 is kept at the base supplied power P1_base, which is set inaccordance with the detected value of the second remaining capacitySOC2. If the base supplied power P1_base is greater than or equal to thesupplied power corresponding to the driving force demand DT_dmd (inother words, if the driving force demand DT_dmd is less than or equal tothe threshold value DT_th4, which is obtained by converting the basesupplied power P1_base into a driving force value of the electric motor100), a supplied power corresponding to the driving force demand DT_dmdwithin the base supplied power P1_base is supplied only from the firstenergy storage device 2 to the electric motor 100 and, at the same time,the surplus supplied power is supplied to charge the second energystorage device 3.

Furthermore, when the driving force demand DT_dmd is less than or equalto the threshold value DT_th2, if the base supplied power P1_base issmaller than the supplied power corresponding to the driving forcedemand DT_dmd (in other words, if the driving force demand DT_dmd islarger than the threshold value DT_th4), the base supplied power P1_baseis fed from the first energy storage device 2 to the electric motor 100,whereas the power deficit is fed from the second energy storage device 3to the electric motor 100.

Thus, when the detected value of the second remaining capacity SOC2falls within the medium remaining capacity, a situation in which poweris supplied from the second energy storage device 3 to the electricmotor 100 is less likely to occur than when the detected value of thesecond remaining capacity SOC2 falls within the high-remaining-capacityarea. In addition, as the second remaining capacity SOC2 decreases, arange for the driving force demand DT_dmd over which power is suppliedfrom the first energy storage device 2 to charge the second energystorage device 3 increases and the charging power used to charge thesecond energy storage device 3 is more likely to increase.

As a result, the second remaining capacity SOC2 can be kept in themedium-remaining-capacity area as much as possible. This can prevent asmuch as possible the progress of deterioration of the second energystorage device 3.

Furthermore, when the driving force demand DT_dmd is less than or equalto the threshold value DT_th2, the base supplied power P1_base to beoutput from the first energy storage device 2 is set in accordance withthe second remaining capacity SOC2 regardless of the driving forcedemand DT_dmd. Thus, the output P2 or the input of the second energystorage device 3 varies in accordance with a change in the driving forcedemand DT_dmd, whereas the output P1 of the first energy storage device2 varies with low sensitivity to changes in the driving force demandDT_dmd.

As a result, the output P1 of the first energy storage device 2 is ofhigh stability with less frequent variations. This can prevent as muchas possible the progress of deterioration of the first energy storagedevice 2.

The determination result of STEP16 is negative within thelow-remaining-capacity area. In this situation, then, in STEP23 (seeFIG. 8), the power transmission controller 41 determines whether or notthe driving force demand DT_dmd is larger than a predetermined thresholdvalue DT_th3.

In an example of this embodiment, the predetermined threshold valueDT_th3 is set to a predetermined constant value. In addition, thethreshold value DT_th3 is set to a driving force value larger than adriving force that can be generated by the electric motor 100 when thebase supplied power P1_base, which is set in the way described above inaccordance with the second remaining capacity SOC2, is fed to theelectric motor 100.

Note that the threshold value DT_th3 may be set so that a supplied powercorresponding to the threshold value DT_th3 becomes equal to theupper-limit supplied power that can be output by the first energystorage device 2 (>P1_base) or a nearby constant value of suppliedpower.

The determination result of STEP23 is affirmative within the shaded areain the low-remaining-capacity area illustrated in FIG. 5. In this case,in STEP24, the power transmission controller 41 controls the powertransmission circuit unit 11 so that the output P1 of the first energystorage device 2 coincides with a predetermined value of supplied powerand so that the output P2 of the second energy storage device 3coincides with the power deficit obtained by subtracting the output P1,which the first energy storage device 2 is responsible for supplying,from the supplied power corresponding to the driving force demandDT_dmd.

In this case, specific control of the power transmission circuit unit 11can be performed in a manner similar to that in STEP14 in FIG. 6.

Accordingly, the supplied power corresponding to the driving forcedemand DT_dmd is fed from both the first energy storage device 2 and thesecond energy storage device 3 to the electric motor 100 in such amanner that the sum of the output P1 of the first energy storage device2 and the output P2 of the second energy storage device 3 coincides withthe supplied power corresponding to the driving force demand DT_dmd. Inthis case, a portion of the supplied power corresponding to the drivingforce demand DT_dmd which the first energy storage device 2 isresponsible for supplying is equal to a predetermined value of suppliedpower.

In this case, the predetermined value of supplied power, which is outputfrom the first energy storage device 2, may be, for example, anupper-limit supplied power that can be output by the first energystorage device 2 or a nearby constant value of supplied power.Alternatively, the predetermined value of supplied power may be asupplied power set to vary depending on either or both of the detectedvalue of the first remaining capacity SOC1 and the detected value of thesecond remaining capacity SOC2.

On the other hand, when the determination result of STEP23 is negative,then, in STEP25, the power transmission controller 41 determines thebase supplied power P1_base, which is a “base” value of the output P1 ofthe first energy storage device 2, in accordance with the detected valueof the second remaining capacity SOC2.

The processing of STEP25 is the same or substantially the same as theprocessing of STEP19. In this embodiment, since the coefficient α is themaximum value “1” within the low-remaining-capacity area, the basesupplied power P1_base, which is determined in STEP25, is equal to themaximum value P1 b.

As in the processing of STEP19, for example, an upper limit of theoutput P1 of the first energy storage device 2 may be set in accordancewith the detected value of the first remaining capacity SOC1 or thelike, and, when the base supplied power P1_base, which is determined inaccordance with the second remaining capacity SOC2, exceeds the upperlimit, the base supplied power P1_base may be forcibly limited to theupper limit.

Alternatively, for example, the base supplied power P1_base may bedetermined, instead of by executing the process illustrated in theflowchart in FIG. 9 in STEP25, directly from the detected value of thesecond remaining capacity SOC2 by using a map created in advance or byusing an operational expression.

After the processing of STEP25 has been executed, then, in STEP26, thepower transmission controller 41 determines whether or not the suppliedpower corresponding to the driving force demand DT_dmd is less than orequal to the base supplied power P1_base. As in the determinationprocessing of STEP20, the determination processing of STEP26 isequivalent to a process of determining whether or not the driving forcedemand DT_dmd is less than or equal to the threshold value DT_th4 (seeFIG. 5), which is obtained by converting the base supplied power P1_baseinto a driving force value in accordance with the detected value of therotational speed of the electric motor 100.

The determination result of STEP26 is affirmative within the diagonallyhatched area in the low-remaining-capacity area illustrated in FIG. 5when the driving force demand DT_dmd is less than or equal to thethreshold value DT_th4. In this situation, in STEP27, the powertransmission controller 41 controls the power transmission circuit unit11 so that the output P1 of the first energy storage device 2 coincideswith the base supplied power P1_base and so that the input (the chargingpower) of the second energy storage device 3 coincides with a suppliedpower corresponding to the surplus power obtained by subtracting thesupplied power corresponding to the driving force demand DT_dmd from thebase supplied power P1_base.

In this case, specific control of the power transmission circuit unit 11can be performed in a manner similar to that in STEP21 in FIG. 7.

Accordingly, the base supplied power P1_base, which is set in the waydescribed above in accordance with the detected value of the secondremaining capacity SOC2, is output from the first energy storage device2 regardless of the driving force demand DT_dmd. In addition, a suppliedpower corresponding to the driving force demand DT_dmd within the basesupplied power P1_base is fed from the first energy storage device 2 tothe electric motor 100 and the surplus supplied power obtained bysubtracting the supplied power corresponding to the driving force demandDT_dmd from the base supplied power P1_base is supplied from the firstenergy storage device 2 to charge the second energy storage device 3.

On the other hand, the determination result of STEP26 is negative withinthe diagonally hatched area in the low-remaining-capacity areaillustrated in FIG. 5 when the driving force demand DT_dmd is largerthan the threshold value DT_th4. In this case, in STEP28, the powertransmission controller 41 controls the power transmission circuit unit11 so that the output P1 of the first energy storage device 2 coincideswith the supplied power corresponding to the driving force demandDT_dmd.

Accordingly, the supplied power corresponding to the driving forcedemand DT_dmd is fed to the electric motor 100 only from the firstenergy storage device 2 without using the second energy storage device3.

The processing of STEP28 can be, specifically, executed in the followingway, for example. A target value for the input voltage of the inverter17 (=the output voltage of the voltage converter 15) is set inaccordance with the detected value of the rotational speed of theelectric motor 100 or the like. In addition, the supplied powercorresponding to the driving force demand DT_dmd is set as the targetvalue for the output power of the voltage converter 15.

Further, the voltage converter 15 is controlled by using a controlsignal (duty signal) so as to realize the target value for the inputvoltage of the inverter 17 and the target value for the output power ofthe voltage converter 15. Also, the inverter 17 is feedback-controlledby using a control signal (duty signal) so as to cause a target currentto flow through the electric motor 100. The target current is a currentthat can realize a target power set in accordance with the driving forcedemand DT_dmd or a target power obtained by limiting the target powerthrough a limiting process (a limiting process for limiting the outputof the first energy storage device 2).

Further, the voltage converter 16 is controlled to be in power supplyinterruption state. Alternatively, the contactor 13 on the second energystorage device 3 side is controlled to be turned off.

As described above, when the detected value of the second remainingcapacity SOC2 falls within the low-remaining-capacity area, power issupplied to the electric motor 100 from an energy storage deviceincluding at least the first energy storage device 2 out of the firstenergy storage device 2 and the second energy storage device 3 duringthe power-running operation of the electric motor 100.

In addition, when the supplied power corresponding to the driving forcedemand DT_dmd is less than or equal to the base supplied power P1_base,the output P1 of the first energy storage device 2 is kept at the basesupplied power P1_base regardless of the driving force demand DT_dmd.Then, a supplied power corresponding to the driving force demand DT_dmdwithin the base supplied power P1_base is supplied only from the firstenergy storage device 2 to the electric motor 100 and, at the same time,the surplus supplied power is used to charge the second energy storagedevice 3. Thus, the input of the second energy storage device 3 variesin accordance with a change in the driving force demand DT_dmd, whereasthe output P1 of the first energy storage device 2 (=P1_base) varieswith low sensitivity to changes in the driving force demand DT_dmd.

In addition, when the supplied power corresponding to the driving forcedemand DT_dmd is larger than the base supplied power P1_base, thesupplied power corresponding to the driving force demand DT_dmd issupplied only from the first energy storage device 2 to the electricmotor 100 until the driving force demand DT_dmd exceeds the thresholdvalue DT_th3. Only when the driving force demand DT_dmd exceeds thethreshold value DT_th3, the second energy storage device 3 isresponsible for supplying a portion of the supplied power correspondingto the driving force demand DT_dmd.

Thus, when the detected value of the second remaining capacity SOC2falls within the low-remaining-capacity area, a situation in which poweris supplied from the second energy storage device 3 to the electricmotor 100 is less likely to occur than when the detected value of thesecond remaining capacity SOC2 falls within the high-remaining-capacityarea or the medium-remaining-capacity area.

In addition, since the base supplied power P1_base is the maximum valueP1 b within the low-remaining-capacity area, a range for the drivingforce demand DT_dmd over which power is supplied from the first energystorage device 2 to charge the second energy storage device 3 and thecharging power are larger than those for the medium-remaining-capacityarea.

As a result, unless a situation in which the driving force demand DT_dmdis larger than the threshold value DT_th3 continues, the secondremaining capacity SOC2 is likely to return from thelow-remaining-capacity area to the medium-remaining-capacity area.

When the supplied power corresponding to the driving force demand DT_dmdis less than or equal to the base supplied power P1_base, furthermore,the base supplied power P1_base to be output from the first energystorage device 2 is set in accordance with the second remaining capacitySOC2 regardless of the driving force demand DT_dmd. In particular, thebase supplied power P1_base is a constant value (=P1 b) within thelow-remaining-capacity area. Thus, the output P1 of the first energystorage device 2 does not vary in accordance with a change in thedriving force demand DT_dmd.

In addition, the output P1 of the first energy storage device 2 is setto a predetermined constant value when the driving force demand DT_dmdis larger than the threshold value DT_th3, which can prevent the outputP1 of the first energy storage device 2 from varying in accordance withthe driving force demand DT_dmd.

As a result, the output P1 of the first energy storage device 2 withinthe low-remaining-capacity area is of high stability with less frequentvariations. This can prevent as much as possible the progress ofdeterioration of the first energy storage device 2.

The normal combined-use control process when the control mode is set tothe first control mode, which is a basic control mode among the first tothird control modes, has been described in detail.

Second Control Mode

There will now be described the normal combined-use control process whenthe control mode is set to the second control mode.

FIG. 11 illustrates, in map form, the relationship in the second controlmode between the second remaining capacity SOC2 and the proportion ofpowers to be output by the first energy storage device 2 and the secondenergy storage device 3 with respect to the amount of electricity to besupplied (the supplied power) to the electric motor 100 in accordancewith the driving force demand DT_dmd of the electric motor 100. In FIG.11, the meanings of the diagonally hatched areas and the shaded areasare similar to those in FIG. 5. In FIG. 11, a two-dot chain lineindicates the line representing the threshold value DT_th4, which isindicated by the broken line in FIG. 5, for comparison with the firstcontrol mode.

The comparison between FIG. 5 illustrating the first control mode andFIG. 11 illustrating the second control mode demonstrates that thesecond control mode is a control mode in which threshold values used todefine the proportion of powers to be output by the first energy storagedevice 2 and the second energy storage device 3 are different from thosein the first control mode.

In the second control mode according to this embodiment, when the secondremaining capacity SOC2 is comparatively low, the second energy storagedevice 3 is more likely to be charged than in the first control mode.When the second remaining capacity SOC2 is comparatively high, a rangefor the driving force demand DT_dmd over which power is supplied fromthe second energy storage device 3 to the electric motor 100 is largerthan that in the first control mode.

More specifically, in the second control mode according to thisembodiment, the threshold value B2_th1 for the second remaining capacitySOC2, which is the upper limit of the medium-remaining-capacity area, isset in advance to a value higher than that in the first control mode.

In addition, the base supplied power P1_base of the first energy storagedevice 2 within the low-remaining-capacity area and themedium-remaining-capacity area of the second energy storage device 3 isdetermined in accordance with the detected value of the second remainingcapacity SOC2 so that the base supplied power P1_base is larger thanthat in the first control mode (in other words, so that the thresholdvalue DT_th4 obtained by converting the base supplied power P1_base intoa driving force value in accordance with the rotational speed of theelectric motor 100 (a value calculated with a constant rotational speed)is larger than that in the first control mode).

The base supplied power P1_base can be determined in a way similar tothat in the first control mode. For example, as in the first controlmode, the base supplied power P1_base (=α×P1 b) can be determined byusing a process similar to the process illustrated in the flowchart inFIG. 9. In this case, however, the maximum value P1 b of the basesupplied power P1_base is set in advance to a value larger than that inthe first control mode. In the second control mode, the maximum value P1b of the base supplied power P1_base may be, for example, an upper-limitsupplied power that can be output from the first energy storage device 2or a nearby supplied power.

The base supplied power P1_base in the second control mode may bedetermined directly from, for example, the detected value of the secondremaining capacity SOC2 by using a map created in advance or by using anoperational expression.

In the second control mode, furthermore, the threshold value DT_th1 forthe driving force demand DT_dmd within the high-remaining-capacity areaand the threshold value DT_th2 for the driving force demand DT_dmdwithin the medium-remaining-capacity area are set to values larger thanthose in the first control mode.

In the example illustrated in FIG. 11, furthermore, the threshold valueDT_th3 for the driving force demand DT_dmd within thelow-remaining-capacity area is set so that the supplied powercorresponding to the threshold value DT_th3 coincides with the basesupplied power P1_base. However, the supplied power corresponding to thethreshold value DT_th3 may be larger than the base supplied powerP1_base so long as the supplied power corresponding to the thresholdvalue DT_th3 is less than or equal to the upper-limit supplied powerthat can be output from the first energy storage device 2.

The way in which threshold values related to the second remainingcapacity SOC2 and the driving force demand DT_dmd in the second controlmode are set is the same or substantially the same as that in the firstcontrol mode, except the particulars described above.

The normal combined-use control process in the second control mode isexecuted in accordance with the flowchart illustrated in FIG. 6 to FIG.8 described above in a way similar to that in the first control mode.Note that the processing of STEP26 and STEP28 in FIG. 8 may be omittedwhen the threshold value DT_th3 for the driving force demand DT_dmdwithin the low-remaining-capacity area is set so that the supplied powercorresponding to the threshold value DT_th3 coincides with the basesupplied power P1_base.

The normal combined-use control process in the second control mode isexecuted in the way described above.

In the second control mode, a remaining capacity area (low-sideremaining capacity area) obtained by combining thelow-remaining-capacity area and the medium-remaining-capacity area islarger than that in the first control mode, and a range for the drivingforce demand DT_dmd over which power is supplied from the first energystorage device 2 to charge the second energy storage device 3 within thelow-side remaining capacity area is larger than that in the firstcontrol mode. Thus, the second remaining capacity SOC2 is more likely tobe kept in a state near the high-remaining-capacity area.

In addition, a range for the driving force demand DT_dmd over whichpower is supplied from the second energy storage device 3 to theelectric motor 100 within the medium-remaining-capacity area and thehigh-remaining-capacity area is also larger than that in the firstcontrol mode.

As a result, when the driving force demand DT_dmd is comparatively large(when the relationship of DT_dmd>DT_th4 holds), the supplied power tothe electric motor 100 can be changed over a wide range for the drivingforce demand DT_dmd with high responsivity to changes in the drivingforce demand DT_dmd. This results in an increase in the responsivity ofthe actual driving force of the electric motor 100 to changes in thedriving force demand DT_dmd.

In this embodiment, the threshold value B2_th1 for the second remainingcapacity SOC2, which is the upper limit of the medium-remaining-capacityarea, and the base supplied power P1_base of the first energy storagedevice 2 are both set to values larger than those in the first controlmode. Alternatively, only one of the threshold value B2_th1 and the basesupplied power P1_base may be set to a value larger than that in thefirst control mode. This also allows the area within which power issupplied from the first energy storage device 2 to change the secondenergy storage device 3 to be larger than that in the first controlmode.

Third Control Mode

There will now be described the normal combined-use control process whenthe control mode is set to the third control mode.

FIG. 12 illustrates, in map form, the relationship in the third controlmode between the second remaining capacity SOC2 and the proportion ofpowers to be output by the first energy storage device 2 and the secondenergy storage device 3 with respect to the amount of electricity to besupplied (the supplied power) to the electric motor 100 in accordancewith the driving force demand DT_dmd of the electric motor 100. In FIG.12, the meanings of the diagonally hatched areas and the shaded areasare similar to those in FIG. 5. In FIG. 12, a two-dot chain lineindicates the line representing the threshold value DT_th4, which isindicated by the broken line in FIG. 5, for comparison with the firstcontrol mode.

The comparison between FIG. 5 illustrating the first control mode andFIG. 12 illustrating the third control mode demonstrates that the thirdcontrol mode is a control mode in which threshold values used to definethe proportion of powers to be output by the first energy storage device2 and the second energy storage device 3 are different from those in thefirst control mode.

In the third control mode according to this embodiment, even when thesecond remaining capacity SOC2 is comparatively low, the second energystorage device 3 is less likely to be charged than in the first controlmode. When the second remaining capacity SOC2 is comparatively high, arange for the driving force demand DT_dmd over which power is suppliedfrom the first energy storage device 2 to the electric motor 100 islarger than that in the first control mode.

More specifically, in the third control mode according to thisembodiment, the threshold value B2_th1 for the second remaining capacitySOC2, which is the upper limit of the medium-remaining-capacity area, isset in advance to a value lower than that in the first control mode.

In addition, the base supplied power P1_base of the first energy storagedevice 2 within the low-remaining-capacity area and themedium-remaining-capacity area of the second energy storage device 3 isdetermined in accordance with the detected value of the second remainingcapacity SOC2 so that the base supplied power P1_base is lower than thatin the first control mode (in other words, so that the threshold valueDT_th4 obtained by converting the base supplied power P1_base into adriving force value in accordance with the rotational speed of theelectric motor 100 (a value calculated with a constant rotational speed)is smaller than that in the first control mode).

The base supplied power P1_base can be determined in a way similar tothat in the first control mode. For example, as in the first controlmode, the base supplied power P1_base (=α×P1 b) can be determined byusing a process similar to the process illustrated in the flowchart inFIG. 9. In this case, however, the maximum value P1 b of the basesupplied power P1_base is set in advance to a value smaller than that inthe first control mode.

The base supplied power P1_base in the third control mode may be setdirectly from, for example, the detected value of the second remainingcapacity SOC2 by using a map created in advance or by using anoperational expression.

In the third control mode, furthermore, the threshold value DT_th1 forthe driving force demand DT_dmd within the high-remaining-capacity areaand the threshold value DT_th2 for the driving force demand DT_dmdwithin the medium-remaining-capacity area are set to values smaller thanthose in the first control mode.

The way in which threshold values related to the second remainingcapacity SOC2 and the driving force demand DT_dmd in the third controlmode are set is the same or substantially the same as that in the firstcontrol mode, except the particulars described above.

The normal combined-use control process in the third control mode isexecuted in accordance with the flowchart illustrated in FIG. 6 to FIG.8 described above in a way similar to that in the first control mode.

The normal combined-use control process in the third control mode isexecuted in the way described above.

In the third control mode, a remaining capacity area (low-side remainingcapacity area) obtained by combining the low-remaining-capacity area andthe medium-remaining-capacity area is smaller than that in the firstcontrol mode, and a range for the driving force demand DT_dmd over whichpower is supplied from the first energy storage device 2 to charge thesecond energy storage device 3 within the low-side remaining capacityarea is smaller than that in the first control mode. Thus, a situationin which power is supplied from the first energy storage device 2 tocharge the second energy storage device 3 is less likely to occur.

The power loss caused by the charging operation described above can bereduced compared to that in the first control mode and the secondcontrol mode. As a result, the amount of electrical energy consumed byall of the first energy storage device 2 and the second energy storagedevice 3 per unit distance of travel of the vehicle can be reducedcompared to that in the first control mode and the second control mode.This results in an extension of the drivable range of the vehicle.

In this embodiment, the threshold value B2_th1 for the second remainingcapacity SOC2, which is the upper limit of the medium-remaining-capacityarea, and the base supplied power P1_base of the first energy storagedevice 2 are both set to values smaller than those in the first controlmode. Alternatively, only one of the threshold value B2_th1 and the basesupplied power P1_base may be set to a value smaller than that in thefirst control mode. This also allows the area within which power issupplied from the first energy storage device 2 to change the secondenergy storage device 3 to be smaller than that in the first controlmode.

A brief summary of the first to third control modes described above ispresented below. The first control mode is a so-called “long-lastingmode”, which is used mainly to let the first energy storage device 2 andthe second energy storage device 3 deteriorate as little as possible.The second control mode is a so-called “sport mode”, which is usedmainly to enhance responsivity to the driving force demand DT_dmd of theelectric motor 100. The third control mode is a so-called “eco mode”,which is used mainly to enhance the fuel economy performance of thevehicle (the distance traveled by the vehicle per unit of electricalenergy consumed).

Extended-Stop Control Process

The extended-stop control process in STEP6 described above will now bedescribed in detail.

In the extended-stop control process, the power transmission controller41 controls the power transmission circuit unit 11 to supply only thedeficit against the supplied power corresponding to the driving forcedemand DT_dmd from the second energy storage device 3 to the electricmotor 100 while supplying power from the first energy storage device 2to the electric motor 100 as continuously as possible during thepower-running operation of the electric motor 100.

In the extended-stop control process, the power transmission controller41 executes a process illustrated in a flowchart in FIG. 13 at intervalsof a predetermined control process period. Specifically, in STEP41, thepower transmission controller 41 determines an upper-limit suppliedpower P1_max that can be output from the first energy storage device 2,in accordance with the detected value of the first remaining capacitySOC1.

The upper-limit supplied power P1_max is determined from the detectedvalue of the first remaining capacity SOC1, for example, in a mannerdepicted on a graph in FIG. 15 by using a map created in advance or byusing an operational expression. The upper-limit supplied power P1_maxis determined to be a value that becomes smaller as the first remainingcapacity SOC1 decreases.

Then, in STEP42, the power transmission controller 41 determines whetheror not the upper-limit supplied power P1_max is larger than the suppliedpower corresponding to the driving force demand DT_dmd.

If the determination result of STEP42 is affirmative, in STEP43, thepower transmission controller 41 controls the power transmission circuitunit 11 so that the output P1 of the first energy storage device 2coincides with the supplied power corresponding to the driving forcedemand DT_dmd.

In this case, specific control of the power transmission circuit unit 11can be performed in a manner similar to that in STEP28 in FIG. 8.

On the other hand, if the determination result of STEP42 is negative, inSTEP44, the power transmission controller 41 controls the powertransmission circuit unit 11 so that the output P1 of the first energystorage device 2 coincides with the upper-limit supplied power P1_maxand so that the output P2 of the second energy storage device 3coincides with the power deficit obtained by subtracting the output P1of the first energy storage device 2 (=P1_max) from the supplied powercorresponding to the driving force demand DT_dmd.

In this case, specific control of the power transmission circuit unit 11can be performed in a manner similar to that in STEP14 in FIG. 6.

In STEP44, when the detected value of the first remaining capacity SOC1has reached the lower limit value B1_min and the upper-limit suppliedpower P1_max=0 holds, the supplied power corresponding to the drivingforce demand DT_dmd is supplied only from the second energy storagedevice 3 to the electric motor 100. In this situation, the voltageconverter 15 of the power transmission circuit unit 11 is controlled tobe in power supply interruption state or the contactor 12 on the firstenergy storage device 2 side is controlled to be turned off.

The extended-stop control process is executed in the way describedabove. In the extended-stop control process, the first energy storagedevice 2 from which it is difficult to output a high supplied power ispreferentially used to supply power to the electric motor 100. Even whenthe upper-limit supplied power P1_max, which can be output by the firstenergy storage device 2, is not sufficient for the supplied powercorresponding to the driving force demand DT_dmd, power is supplied fromboth the first energy storage device 2 and the second energy storagedevice 3 to the electric motor 100, allowing the first energy storagedevice 2 to be discharged to the remaining capacity corresponding to thelower limit value B1_min.

Thereafter, the second energy storage device 3 from which it is easy tooutputs a high supplied power is used to supply power to the electricmotor 100. This allows the second energy storage device 3 to bedischarged to the remaining capacity corresponding to the lower limitvalue B2_min or to a nearby remaining capacity.

An example of changes in the first remaining capacity SOC1 and thesecond remaining capacity SOC2 through the normal combined-use controlprocess and extended-stop control process described above will now bedescribed with reference to FIG. 14 to FIG. 16.

In the illustrated example, the control mode in the normal combined-usecontrol process is the first control mode, by way of example.

FIG. 14 illustrates a graph S, which depicts, by way of example, inwhich pattern the combination of the first remaining capacity SOC1 andthe second remaining capacity SOC2 changes when the vehicle is travelingwith the normal combined-use control process being executed.

The graph S demonstrates that the second remaining capacity SOC2increases or decreases so as to be kept at, for example, a value nearthe threshold value B2_th1 by appropriately charging the second energystorage device 3 with power supplied from the first energy storagedevice 2, whereas the first remaining capacity SOC1 decreases.

In FIG. 14, thick-line arrows a1 to a4 indicate how the combination ofthe first remaining capacity SOC1 and the second remaining capacity SOC2changes when the vehicle starts cruising at, for example, the time point(time t0) at which the combination of the first remaining capacity SOC1and the second remaining capacity SOC2 is in a state indicated by apoint Q. Cruising is movement of a vehicle with the driving force demandDT_dmd of the electric motor 100 and the rotational speed being keptsubstantially constant.

In FIG. 15, a point b1 and thick-line arrows b2 to b4 indicate changesin the first remaining capacity SOC1 from the time t0. In FIG. 16,thick-line arrows c1 and c2, a point c3, and a thick-line arrow c4indicate changes in the second remaining capacity SOC2 from the time to.

The indications a1, b1, and c1 represent the time period from the timet0 to time t1, the indications a2, b2, and c2 represent the time periodfrom the time t1 to time t2, the indications a3, b3, and c3 representthe time period from the time t2 to time t3, and the indications a4, b4,and c4 represent the time period after the time t3. The time t3 is atime at which the extended-stop control process is started in responseto the first remaining capacity SOC1 reaching the threshold valueB1_th1. In addition, the driving force demand DT_dmd of the electricmotor 100 which is cruising has a value positioned at the heightindicated by c1, c2, c3, and c4 in FIG. 16, for example.

During the time period from the time t0 to the time t1, through thenormal combined-use control process in the first control mode, no poweris supplied from the first energy storage device 2 to the electric motor100 or nor is the second energy storage device 3 charged with powersupplied from the first energy storage device 2, and power is suppliedonly from the second energy storage device 3 to the electric motor 100(see FIG. 16). Thus, as indicated by way of example by the arrow a1 inFIG. 14 and the point b1 in FIG. 15, the first remaining capacity SOC1is kept constant. In addition, as indicated by way of example by thearrow a1 in FIG. 14 and the arrow c1 in FIG. 16, the second remainingcapacity SOC2 decreases.

When the second remaining capacity SOC2 reaches the threshold valueB2_th1 at the time t1, then, during the time period from the time t1 tothe time t2, through the normal combined-use control process in thefirst control mode, power is supplied from both the first energy storagedevice 2 and the second energy storage device 3 to the electric motor100 (see FIG. 16). Thus, as indicated by way of example by the arrow a2in FIG. 14 and the arrow b2 in FIG. 15, the first remaining capacitySOC1 decreases and, as indicated by way of example by the arrow a2 inFIG. 14 and the arrow c2 in FIG. 16, the second remaining capacity SOC2decreases.

When the second remaining capacity SOC2 reaches the value correspondingto the point c3 in FIG. 16 at the time t2, through the normalcombined-use control process in the first control mode, power issupplied only from the first energy storage device 2 to the electricmotor 100. Thus, during the time period from the time t2 to the time t3,as indicated by way of example by the arrow a3 in FIG. 14 and the pointc3 in FIG. 16, the second remaining capacity SOC2 is kept constant.Then, as indicated by way of example by the arrow a3 in FIG. 14 and thearrow b3 in FIG. 15, the first remaining capacity SOC1 decreases.

When the first remaining capacity SOC1 decrease to the threshold valueB1_th1 at the time t3, the extended-stop control process is started.Thus, after the time t3, as indicated by way of example by the arrow a4in FIG. 14 and the arrow b4 in FIG. 15, the first remaining capacitySOC1 decreases to the lower limit value B1_min while the first energystorage device 2 outputs the upper-limit supplied power P1_max. Inaddition, as indicated by way of example by the arrow a4 in FIG. 14 andthe arrow c4 in FIG. 16, the second remaining capacity SOC2 decreases tothe lower limit value B2_min.

FIG. 17 illustrates an example of changes in the first remainingcapacity SOC1 and the second remaining capacity SOC2 over time in theextended-stop control process. The illustrated example provides anexample of changes in the first remaining capacity SOC1 and the secondremaining capacity SOC2 over time when the output (the supplied power)to the electric motor 100 is kept at a certain constant value (that is,when the vehicle is cruising) after the start of the extended-stopcontrol process.

As illustrated in FIG. 17, power is supplied from both the first energystorage device 2 and the second energy storage device 3 to the electricmotor 100, thereby ensuring a constant value of supplied power to theelectric motor 100 and also allowing the respective remaining capacitiesSOC1 and SOC2 of the first energy storage device 2 and the second energystorage device 3 to be consumed to the respective lower limit valuesB1_min and B2_min.

In the manner described above, an extension of the period during whichpower can be supplied to the electric motor 100 with the use of both thefirst energy storage device 2 and the second energy storage device 3allows the power of both the first energy storage device 2 and thesecond energy storage device 3 to be exhausted more fully than anextension of the period during which power can be supplied to theelectric motor 100 with the use of either energy storage device (e.g.,the first energy storage device 2). This can result in a furtherextension of the period during which power can be supplied to theelectric motor 100, leading to an extension of the drivable range of thevehicle.

As described above, in particular, in the normal combined-use controlprocess in the first control mode, the first remaining capacity SOC1 canbe reduced while the second remaining capacity SOC2 is held in themedium-remaining-capacity area or at a nearby value.

In the extended-stop control process, furthermore, the first energystorage device 2 and the second energy storage device 3 can bedischarged fully to the respective lower limit values B1_min and B2_minor to nearby remaining capacity values to supply power to the electricmotor 100.

Control Process During Regenerative Operation

There will now be described a control process for the power transmissioncontroller 41 during the regenerative operation of the electric motor100.

In this embodiment, the control process for the power transmissioncontroller 41 during the regenerative operation of the electric motor100 is executed at intervals of a predetermined control process periodin a way illustrated in a flowchart in FIG. 18.

Specifically, in STEP51, the power transmission controller 41 acquires adetected value of the second remaining capacity SOC2 and a regenerationdemand G_dmd of the electric motor 100. In this embodiment, theregeneration demand G_dmd is a request value for power to be generatedby the electric motor 100 (an amount of energy generated per unit time).

The regeneration demand G_dmd is determined from, for example, a brakingforce demand during the regenerative operation of the electric motor 100and a detected value of the rotational speed of the electric motor 100by using a map created in advance or by using an operational expression.

Then, in STEP52, the power transmission controller 41 determines therespective target inputs Pc1 and Pc2 (target charging powers) of thefirst energy storage device 2 and the second energy storage device 3from the detected value of the second remaining capacity SOC2 and theregeneration demand G_dmd of the electric motor 100 on the basis of amap created in advance.

FIG. 19 illustrates a visual representation of the map. On the map, ashaded area within which the regeneration demand G_dmd is less than orequal to a predetermined threshold value G_th1 represents an area withinwhich only the second energy storage device 3 is charged (an area withinwhich Pc1=0 holds), and a diagonally hatched area within which theregeneration demand G_dmd is larger than the threshold value G_th1represents an area within which both the first energy storage device 2and the second energy storage device 3 are charged.

The threshold value G_th1 is a threshold value set in accordance withthe detected value of the second remaining capacity SOC2. In theillustrated example, the threshold value G_th1 is a predeterminedconstant value (fixed value) in an area within which the secondremaining capacity SOC2 is less than or equal to a predetermined valueSOC2 a, and is set to decrease in accordance with an increase in thesecond remaining capacity SOC2 in an area within which the secondremaining capacity SOC2 is larger than the predetermined value SOC2 a.The threshold value G_th1 in the area within which the second remainingcapacity SOC2 is less than or equal to the predetermined value SOC2 a isset to a value near a maximum value G_max of the regeneration demandG_dmd.

In STEP52, when the combination of the detected value of the secondremaining capacity SOC2 and the regeneration demand G_dmd falls withinthe shaded area, the target input Pc1 of the first energy storage device2 is set to zero and the regeneration demand G_dmd is set as the targetinput Pc2 of the second energy storage device 3. Accordingly, if theregeneration demand G_dmd is smaller than the threshold value G_th1, thetarget inputs Pc1 and Pc2 are set so that only the second energy storagedevice 3 is charged with regenerative power.

When the combination of the detected value of the second remainingcapacity SOC2 and the regeneration demand G_dmd falls within thediagonally hatched area, a regenerative value that coincides with thethreshold value G_th1 is set as the target input Pc2 of the secondenergy storage device 3 and the residual regenerative value, which isobtained by subtracting the target input Pc2 of the second energystorage device 3 from the regeneration demand G_dmd, is set as thetarget input Pc1 of the first energy storage device 2.

Accordingly, when the regeneration demand G_dmd is larger than thethreshold value G_th1 and when the detected value of the secondremaining capacity SOC2 is larger than the predetermined value SOC2 a,the target inputs Pc1 and Pc2 are set so that the ratio of the targetinput Pc2 of the second energy storage device 3 to the regenerationdemand G_dmd decreases as the detected value of the second remainingcapacity SOC2 increases (in other words, so that the ratio of the targetinput Pc1 of the first energy storage device 2 to the regenerationdemand G_dmd increases as the detected value of the second remainingcapacity SOC2 increases).

Then, in STEP53, the power transmission controller 41 determines whetheror not the regeneration demand G_dmd is larger than the threshold valueG_th1.

The determination result of STEP53 is affirmative within the diagonallyhatched area illustrated in FIG. 19. In this situation, in STEP54, thepower transmission controller 41 controls the power transmission circuitunit 11 so that the first energy storage device 2 and the second energystorage device 3 are charged with the target inputs Pc1 and Pc2,respectively.

The processing of STEP54 can be, specifically, executed in the followingway, for example. A target value for the output voltage of the inverter17 (=the input voltages of the voltage converters 15 and 16) is set inaccordance with the detected value of the rotational speed of theelectric motor 100 or the like. In addition, the target input Pc1 is setas the target value for the output power from the voltage converter 15to the first energy storage device 2, and the target input Pc2 is set asthe target value for the output power from the voltage converter 16 tothe second energy storage device 3.

Further, the inverter 17 is controlled so as to realize the target valuefor the output voltage of the inverter 17. Also, the voltage converters15 and 16 are controlled so as to realize the target value for theoutput power from the voltage converter 15 to the first energy storagedevice 2 and the target value for the output power from the voltageconverter 16 to the second energy storage device 3.

On the other hand, the determination result of STEP53 is negative withinthe shaded area illustrated in FIG. 19. In this situation, in STEP55,the power transmission controller 41 controls the power transmissioncircuit unit 11 so that only the second energy storage device 3 ischarged with the target input Pc2.

The processing of STEP55 can be, specifically, executed in the followingway, for example. A target value for the output voltage of the inverter17 (=the input voltage of the voltage converter 16) is set in accordancewith the detected value of the rotational speed of the electric motor100 or the like. In addition, the target input Pc2 is set as the targetvalue for the output power from the voltage converter 16 to the secondenergy storage device 3.

Further, the inverter 17 is controlled so as to realize the target valuefor the output voltage of the inverter 17. Also, the voltage converter16 is controlled so as to realize the target value for the output powerfrom the voltage converter 16 to the second energy storage device 3.

Furthermore, the voltage converter 15 is controlled to be in powersupply interruption state. Alternatively, the contactor 12 on the firstenergy storage device 2 side is controlled to be turned off. Thisprohibits discharging from the first energy storage device 2.

In the way described above, the control process for the powertransmission controller 41 during the regenerative operation of theelectric motor 100 is executed.

The control process for the power transmission controller 41 during theregenerative operation is executed in the way described above, therebyallowing regenerative power to be supplied to basically charge thesecond energy storage device 3. Only an excess of regenerative powerused to charge the second energy storage device 3 (a regenerative valueexceeding the threshold value G_th1) is used to charge the first energystorage device 2.

This allows the second remaining capacity SOC2 to be kept in themedium-remaining-capacity area or at a nearby remaining capacity valuewhile minimizing the occurrence of a situation in which the secondenergy storage device 3 needs to be charged with power supplied by thefirst energy storage device 2.

In addition, the first energy storage device 2 is typically low inresistance to charging at high rates (high-speed charging in which thecharging power per unit time is large). The regenerative value for thefirst energy storage device 2 is reduced as much as possible, which canprevent as much as possible deterioration of the first energy storagedevice 2.

The correspondence between components illustrated in the firstembodiment described above and components disclosed herein will bebriefly explained below.

In this embodiment, the driving force demand DT_dmd of the electricmotor 100 (electric load) corresponds to an output demand disclosedherein. The threshold value B1_th1 for the first remaining capacity SOC1corresponds to a first threshold value disclosed herein, and the lowerlimit value B1_min of the first remaining capacity SOC1 corresponds to asecond threshold value disclosed herein. The threshold value B2_th1 forthe second remaining capacity SOC2 corresponds to a fourth thresholdvalue disclosed herein, and the lower limit value B2_min of the secondremaining capacity SOC2 corresponds to a third threshold value disclosedherein.

The threshold value DT_th4 for the driving force demand DT_dmd (athreshold value obtained by converting the base supplied power P1_baseinto a driving force value) corresponds to an A-th threshold valuedisclosed herein.

The normal combined-use control process (the processing of STEP4)corresponds to a control process based on a first control rule disclosedherein. The processing of STEP21 and STEP27 in the normal combined-usecontrol process corresponds to a process for controlling the powertransmission circuit unit 11 to charge the second energy storage device3 with a portion of the output of the first energy storage device 2.

The extended-stop control process (the processing of STEP6) correspondsto a control process based on a second control rule disclosed herein.

Second Embodiment

Next, a second embodiment of the present disclosure will be describedwith reference to FIG. 20 and FIG. 21. This embodiment is the same orsubstantially the same as the first embodiment, except for a controlprocess performed during the regenerative operation of the electricmotor 100. Thus, the same or substantially the same portions as those inthe first embodiment are not described herein.

In this embodiment, the control process for the power transmissioncontroller 41 during the regenerative operation of the electric motor100 is executed at intervals of a predetermined control process periodin a way illustrated in a flowchart in FIG. 20.

Specifically, in STEP61, the power transmission controller 41 acquires adetected value of the second remaining capacity SOC2 and a regenerationdemand G_dmd of the electric motor 100. The processing of STEP61 is thesame or substantially the same as the processing of STEP51 in the firstembodiment.

Then, in STEP62, the power transmission controller 41 determines therespective target inputs Pc1 and Pc2 (target charging powers) of thefirst energy storage device 2 and the second energy storage device 3from the detected value of the second remaining capacity SOC2 and theregeneration demand G_dmd of the electric motor 100 on the basis of amap created in advance.

FIG. 21 illustrates a visual representation of the map in thisembodiment. On the map, a diagonally hatched area within which theregeneration demand G_dmd is less than or equal to a predeterminedthreshold value G_th2 represents an area within which only the firstenergy storage device 2 is charged (an area within which Pc2=0 holds),and a shaded area within which the regeneration demand G_dmd is largerthan the threshold value G_th2 and is less than or equal to apredetermined threshold value G_th1 and a diagonally hatched area withinwhich the regeneration demand G_dmd is larger than the threshold valueG_th1 represent an area within which both the first energy storagedevice 2 and the second energy storage device 3 are charged.

Of the threshold values G_th1 and G_th2, the threshold value G_th1 is athreshold value set in accordance with the detected value of the secondremaining capacity SOC2, as in the first embodiment.

In this embodiment, the threshold value G_th2 is a predeterminedconstant value that has been determined in advance. The threshold valueG_th2 is a comparatively small value (a near-zero value).

In STEP62, when the combination of the detected value of the secondremaining capacity SOC2 and the regeneration demand G_dmd falls withinthe bottom diagonally hatched area, the target input Pc2 of the secondenergy storage device 3 is set to zero and the regeneration demand G_dmdis set as the target input Pc1 of the first energy storage device 2.

Accordingly, the target inputs Pc1 and Pc2 are set so that only thefirst energy storage device 2 is charged with regenerative power.

When the combination of the detected value of the second remainingcapacity SOC2 and the regeneration demand G_dmd falls within the shadedarea, a regenerative value that coincides with the threshold value G_th2is set as the target input Pc1 of the first energy storage device 2 andthe residual regenerative value, which is obtained by subtracting thetarget input Pc1 of the first energy storage device 2 from theregeneration demand G_dmd, is set as the target input Pc2 of the secondenergy storage device 3.

When the combination of the detected value of the second remainingcapacity SOC2 and the regeneration demand G_dmd falls within the topdiagonally hatched area, a supplied power that coincides with thethreshold value G_th1 is set as the target input Pc2 of the secondenergy storage device 3 and the residual regenerative value, which isobtained by subtracting the target input Pc2 of the second energystorage device 3 from the regeneration demand G_dmd, is set as thetarget input Pc1 of the first energy storage device 2.

Then, in STEP63, the power transmission controller 41 determines whetheror not the regeneration demand G_dmd is less than or equal to thethreshold value G_th2.

The determination result of STEP63 is affirmative within the bottomdiagonally hatched area illustrated in FIG. 21. In this situation, inSTEP64, the power transmission controller 41 controls the powertransmission circuit unit 11 so that only the first energy storagedevice 2 is charged with the target input Pc1.

The processing of STEP64 can be, specifically, executed in the followingway, for example. A target value for the output voltage of the inverter17 (=the input voltage of the voltage converter 15) is set in accordancewith the detected value of the rotational speed of the electric motor100 or the like. In addition, the target input Pc1 is set as the targetvalue for the output power from the voltage converter 15 to the firstenergy storage device 2.

Further, the inverter 17 is controlled so as to realize the target valuefor the output voltage of the inverter 17. Also, the voltage converter15 is controlled so as to realize the target value for the output powerfrom the voltage converter 15 to the first energy storage device 2.

Furthermore, the voltage converter 16 is controlled to be in powersupply interruption state. Alternatively, the contactor 13 on the secondenergy storage device 3 side is controlled to be turned off. Thisprohibits discharging from the second energy storage device 3.

On the other hand, the determination result of STEP63 is negative withinthe shaded area or the top diagonally hatched area illustrated in FIG.21. In this situation, in STEP65, the power transmission controller 41controls the power transmission circuit unit 11 so that the first energystorage device 2 and the second energy storage device 3 are charged withthe target inputs Pc1 and Pc2, respectively.

In this case, specific control of the power transmission circuit unit 11can be performed in a manner similar to that in the processing of STEP54in the first embodiment.

In this embodiment, the control process for the power transmissioncontroller 41 during the regenerative operation of the electric motor100 is executed in the way described above.

The control process for the power transmission controller 41 during theregenerative operation is executed in the way described above, therebyallowing a small amount of regenerative power less than or equal to thethreshold value G_th2 to be supplied to charge the first energy storagedevice 2, except for the case where the regeneration demand G_dmd islarger than the threshold value G_th1. In this case, since the chargingpower used to charge the first energy storage device 2 is small, thefirst energy storage device 2 can be charged at a low charging rate (lowrate). This allows the first energy storage device 2 to be charged whilepreventing the progress of deterioration of the first energy storagedevice 2 during the regenerative operation. Hence, the drivable range ofthe vehicle can be extended.

In addition, an amount of regenerative power exceeding the thresholdvalue G_th2 is supplied to charge the second energy storage device 3.This allows the second remaining capacity SOC2 to be kept in themedium-remaining-capacity area or at a nearby remaining capacity valuewhile reducing the occurrence of the situation in which the secondenergy storage device 3 needs to be charged with power supplied by thefirst energy storage device 2.

The correspondence between components illustrated in this embodiment andcomponents disclosed herein are the same as those in the firstembodiment.

Third Embodiment

Next, a third embodiment of the present disclosure will be describedwith reference to FIG. 22. This embodiment is the same or substantiallythe same as the second embodiment, except for a control processperformed during the regenerative operation of the electric motor 100.Thus, the same or substantially the same portions as those in the firstembodiment are not described herein.

In this embodiment, the control process for the power transmissioncontroller 41 during the regenerative operation of the electric motor100 is executed at intervals of a predetermined control process periodin a way illustrated in a flowchart in FIG. 22.

Specifically, in STEP71, the power transmission controller 41 acquires adetected value of the second remaining capacity SOC2 and a regenerationdemand G_dmd of the electric motor 100. The processing of STEP71 is thesame or substantially the same as the processing of STEP51 in the firstembodiment.

Then, in STEP72, the power transmission controller 41 determines therespective target inputs Pc1 and Pc2 (target charging powers) of thefirst energy storage device 2 and the second energy storage device 3from the detected value of the second remaining capacity SOC2 and theregeneration demand G_dmd of the electric motor 100 on the basis of amap created in advance.

In this case, the map used in this embodiment (how areas are separatedby the threshold values G_th1 and G_th2) is the same or substantiallythe same as that in the second embodiment (illustrated in FIG. 21). Inthis embodiment, however, the energy storage device to be charged in theshaded area within which the regeneration demand G_dmd is larger thanthe threshold value G_th2 and is less than or equal to the thresholdvalue G_th1 is different from that in the second embodiment.

In this embodiment, the shaded area illustrated in FIG. 21 is an areawithin which only the second energy storage device 3 is charged. Whenthe combination of the detected value of the second remaining capacitySOC2 and the regeneration demand G_dmd falls within the shaded areaillustrated in FIG. 21, the target input Pc1 of the first energy storagedevice 2 is set to zero and the regeneration demand G_dmd is set as thetarget input Pc2 of the second energy storage device 3.

The method of setting the target inputs Pc1 and Pc2 within the bottomdiagonally hatched area and the top diagonally hatched area illustratedin FIG. 21 is the same or substantially the same as that in the secondembodiment.

Then, in STEP73, the power transmission controller 41 determines whetheror not the regeneration demand G_dmd is less than or equal to thethreshold value G_th2.

The determination result of STEP73 is affirmative within the bottomdiagonally hatched area illustrated in FIG. 21. In this situation, inSTEP74, the power transmission controller 41 controls the powertransmission circuit unit 11 so that only the first energy storagedevice 2 is charged with the target input Pc1.

In this case, specific control of the power transmission circuit unit 11can be performed in a manner similar to that in the processing of STEP64in the second embodiment.

On the other hand, when the determination result of STEP73 is negative,then, in STEP75, the power transmission controller 41 further determineswhether or not the regeneration demand G_dmd is larger than thethreshold value G_th1.

The determination result of STEP75 is affirmative within the topdiagonally hatched area illustrated in FIG. 21. In this situation, inSTEP76, the power transmission controller 41 controls the powertransmission circuit unit 11 so that the first energy storage device 2and the second energy storage device 3 are charged with the targetinputs Pc1 and Pc2, respectively.

In this case, specific control of the power transmission circuit unit 11can be performed in a manner similar to that in the processing of STEP54in the first embodiment.

The determination result of STEP75 is negative within the shaded areaillustrated in FIG. 21. In this case, in STEP77, the power transmissioncontroller 41 controls the power transmission circuit unit 11 so thatonly the second energy storage device 3 is charged with the target inputPc2.

In this case, specific control of the power transmission circuit unit 11can be performed in a manner similar to that in the processing of STEP55in the first embodiment.

In this embodiment, the control process for the power transmissioncontroller 41 during the regenerative operation of the electric motor100 is executed in the way described above.

The control process for the power transmission controller 41 during theregenerative operation is executed in the way described above, therebyallowing, when the regeneration demand G_dmd is a small regenerativevalue less than or equal to the threshold value G_th2, the smallregenerative value to be supplied to charge the first energy storagedevice 2. In this case, as in the second embodiment, the first energystorage device 2 can be charged slowly at a low charging rate. Thisallows the first energy storage device 2 to be charged while preventingthe progress of deterioration of the first energy storage device 2.Hence, the drivable range of the vehicle can be extended.

When the regeneration demand G_dmd is larger than the threshold valueG_th2, regenerative power corresponding to the regeneration demand G_dmdis supplied to charge only the second energy storage device 3 so long asthe threshold value G_th1 is not exceeded. In this case, even if thesecond energy storage device 3 is not charged at a low charging rate,the progress of deterioration of the second energy storage device 3 isless likely to occur. This can facilitate rapid charging of the secondenergy storage device 3. This enables the power transmission circuitunit 11 to be controlled with high stability during the regenerativeoperation.

The correspondence between components illustrated in this embodiment andcomponents disclosed herein are the same as those in the firstembodiment.

As a supplementary explanation, in the second or third embodiment, whenthe regeneration demand G_dmd is larger than the threshold value G_th1,a regenerative value corresponding to the difference between thethreshold value G_th1 and the threshold value G_th2 (a regenerativevalue corresponding to the difference obtained by subtracting aregenerative value that coincides with the threshold value G_th2 from aregenerative value that coincides with the threshold value G_th1) may beset as the target input Pc2 of the second energy storage device 3 andthe residual regenerative value, which is obtained by subtracting thetarget input Pc2 of the second energy storage device 3 from theregeneration demand G_dmd, may be set as the target input Pc1 of thefirst energy storage device 2.

Modifications

There will now be described some modifications to the first to thirdembodiments described above.

The embodiments described above provide the power supply system 1, whichis configured to control the power transmission circuit unit 11 by usingthree control modes, namely, the first to third control modes. Thenumber of control modes of the power transmission circuit unit 11 may betwo or more than three. Alternatively, the power supply system 1 may beconfigured to control the power transmission circuit unit 11 by usingonly one of the first to third control modes.

In different control modes, only one of the base supplied power P1_baseand the threshold value B2_th1 related to the second remaining capacitymay be different. For example, a control mode in which only one of themaximum value P1 b of the base supplied power P1_base and the thresholdvalue B2_th1 is different from that in the first control mode may beadditionally used or may be used in place of the second control mode orthe third control mode.

In the embodiments described above, furthermore, when the detected valueof the first remaining capacity SOC1 is smaller than the lower limitvalue B1_min or when the detected value of the second remaining capacitySOC2 is smaller than the lower limit value B2_min, the stop process isexecuted to prohibit power from being supplied from the correspondingone of the energy storage devices 2 and 3.

However, for example, when the detected value of the first remainingcapacity SOC1 is reduced to the lower limit value B1_min but thedetected value of the second remaining capacity SOC2 is still largerthan the lower limit value B2_min, power may be supplied only from thesecond energy storage device 3 to the electric motor 100 so long as thesupplied power corresponding to the driving force demand DT_dmd can beoutput.

In addition, the control process during the regenerative operation maybe omitted.

In addition, when a specific control mode among the first to thirdcontrol modes is set for the control device 5, both the first energystorage device 2 and the second energy storage device 3 may beprohibited from being charged with regenerative power during theregenerative operation of the electric motor 100 to prevent as much aspossible the progress of deterioration of both the first energy storagedevice 2 and the second energy storage device 3. In this case, forexample, the control device 5 may control the inverter 17 to be in powersupply interruption state, control both the voltage converters 15 and 16to be in power supply interruption state, or control both the contactors12 and 13 to be turned off in order to prohibit the electric motor 100from supplying regenerative power to charge both the energy storagedevices 2 and 3.

This can avoid the progress of deterioration of the first energy storagedevice 2 and the second energy storage device 3 due to their chargingprocedures during the regenerative operation of the electric motor 100.In particular, when the first control mode is set, the progress ofdeterioration of both the energy storage devices 2 and 3 can effectivelybe delayed by prohibiting both the energy storage devices 2 and 3 frombeing charged with regenerative power.

In a plurality of control modes among the first to third control modesor in all the control modes, both the energy storage devices 2 and 3 maybe prohibited from being charged with regenerative power.

In the embodiments described above, furthermore, the driving forcedemand DT_dmd of the electric motor 100 is used as the output demand ofthe electric motor 100 (electric load). Alternatively, for example, anamount of energy to be supplied to the electric motor 100 per unit timein response to the driving force demand DT_dmd or a request value forthe current flowing through the electric motor 100 (the request valuefor the amount of charge per unit time) which corresponds to the drivingforce demand DT_dmd may be used as the output demand of the electricmotor 100 (electric load).

In the embodiments described above, furthermore, the electric load isthe electric motor 100, by way of example but not limited. The electricload may be an electric actuator other than the electric motor 100, ormay be an electrical device that does not output any mechanical power.

In addition, a transportation device in which the power supply system 1is mounted is not limited to an electrically driven vehicle. Thetransportation device may be a hybrid vehicle, for example, or may be aship, a railway vehicle, or any other device.

A power supply system according to an aspect of the present disclosureincludes a first energy storage device, a second energy storage devicehaving a higher power density and a lower energy density than the firstenergy storage device, a power transmission circuit unit, and a controldevice configured to have a function of controlling the powertransmission circuit unit (a first aspect of the present disclosure).The power transmission circuit unit is disposed in a power transmissionpath among an electric load, the first energy storage device, and thesecond energy storage device. The electric load is activated upon beingsupplied with power from at least one of the first energy storage deviceand the second energy storage device. The power transmission circuitunit is configured to be capable of controlling power transmission amongthe electric load, the first energy storage device, and the secondenergy storage device in accordance with a given control signal. Thecontrol device is configured to acquire a first remaining capacity thatis a remaining capacity of the first energy storage device, and isconfigured to control the power transmission circuit unit to perform acontrol process based on a first control rule to supply power from atleast one of the first energy storage device and the second energystorage device to the electric load when the first remaining capacity islarger than a predetermined first threshold value, perform a controlprocess based on a second control rule different from the first controlrule to supply power from one or both of the first energy storage deviceand the second energy storage device to the electric load, the one orboth of the first energy storage device and the second energy storagedevice including at least the first energy storage device, when thefirst remaining capacity is smaller than the first threshold value, andprohibit power from being supplied from at least the first energystorage device to the electric load when the first remaining capacity issmaller than a predetermined second threshold value smaller than thefirst threshold value.

Certain terms as used herein will be briefly explained below. The term“supplied power” refers to an amount of electricity to be supplied to anobject to be supplied with power. The object to be supplied with poweris not limited to the electric load described above and might be anenergy storage device (the first energy storage device or the secondenergy storage device) or any other device such as a capacitive element.In addition, the “output” of the first energy storage device or thesecond energy storage device refers to an amount of power to be suppliedwhich is output from the first energy storage device or the secondenergy storage device. The “electricity”, the “supplied power”, and the“output” of each energy storage device are each expressed as an amountof electrical energy per unit time (e.g., a value of (electric) power)or as an amount of charge per unit time (e.g., a value of current), forexample.

The “output demand” of an electric load refers to an expression thatspecifies a request value for an amount of electricity required toactivate the electric load. The request value for the amount ofelectricity itself may be used as the “output demand”. For example, ifthe electric load is designed to generate a mechanical output (dynamicor kinetic energy) corresponding to the amount of electricity to besupplied to the electric load, a request value for the mechanical outputmay be used as the “output demand” of the electric load.

The term “supplied power corresponding to the ‘output demand’” refers toan amount of power to be supplied to the electric load to meet the“output demand”. The supplied power corresponding to a certain thresholdvalue (such as an A-th threshold value described below) related to anoutput demand refers to an amount of power to be supplied whichcorresponds to the output demand when the output demand is made tocoincide with the threshold value.

Furthermore, what is meant by the “power transmission circuit unit”which is capable of controlling power transmission among the electricload, the first energy storage device, and the second energy storagedevice is that the “power transmission circuit unit” at least has afunction of being capable of controlling the amount of power to besupplied from each of the first energy storage device and the secondenergy storage device to the electric load or that the “powertransmission circuit unit” has, in addition to the function describedabove, a function of being capable of performing selective switchingcontrol of the source and target of power among the electric load, thefirst energy storage device, and the second energy storage device.

Based on the terms defined above, exemplary embodiments of the presentdisclosure will now be described.

According to the first aspect of the present disclosure, the controldevice controls the power transmission circuit unit by using a controlprocess based on different control rules when the first remainingcapacity is larger than the first threshold value and when the firstremaining capacity is smaller than the first threshold value. Thisallows power to be supplied to the electric load by using a controlprocess suitable for conditions with the first remaining capacity beinglow.

In the control process based on the second control rule, power issupplied from one or both of the first energy storage device and thesecond energy storage device to the electric load, the one or both ofthe first energy storage device and the second energy storage deviceincluding at least the first energy storage device. This allows thesecond energy storage device to compensate for a deficit of powersupplied from the first energy storage device, while supplying powerfrom the first energy storage device to the electric load, if thesupplied power from the first energy storage device is insufficient forthe supplied power corresponding to an output demand of the electricload.

Thus, power can be supplied to the electric load in such a manner thatthe remaining capacity of the first energy storage device (firstremaining capacity) is further reduced within a range lower than thefirst threshold value.

This may allow as much energy as possible to be supplied from two energystorage devices to the electric load to enhance the efficiency of use ofthe energy. This makes it possible to extend the period during which thesupplied power corresponding to the output demand can be supplied to theelectric load.

When the first remaining capacity is smaller than the second thresholdvalue, power is prohibited from being supplied from the first energystorage device to the electric load. This prevents the first energystorage device from being over-discharged. Thus, the progress ofdeterioration of the first energy storage device can be prevented.

In the first aspect of the present disclosure, more specifically,preferably, the control device is configured to acquire an output demandof the electric load, and is configured to control the powertransmission circuit unit to set, in the control process based on thesecond control rule, a target value for a supplied power which is to beoutput from the first energy storage device in accordance with the firstremaining capacity, when the target value is smaller than a suppliedpower corresponding to the output demand, output a supplied power equalto the target value from the first energy storage device and output fromthe second energy storage device a supplied power equal to a differenceobtained by subtracting the target value from the supplied powercorresponding to the output demand, and, when the target value isgreater than or equal to the supplied power corresponding to the outputdemand, output the supplied power corresponding to the output demandfrom the first energy storage device (a second aspect of the presentdisclosure).

Accordingly, in the control process based on the second control rule,power is supplied from the first energy storage device to the electricload regardless of whether a target value for a supplied power which isto be output from the first energy storage device is larger or smallerthan the output demand. If the target value is smaller than the outputdemand, the power deficit is compensated for by the second energystorage device.

Since the target value is set in accordance with the remaining capacityof the first energy storage device (first remaining capacity), thetarget value can be set to an upper limit that can be output from thefirst energy storage device or to a nearby value.

Thus, the control process based on the second control rule allows powerto be appropriately supplied from the first energy storage device to theelectric load until the first remaining capacity is reduced to thesecond threshold value.

In the first or second aspect of the present disclosure, preferably, thefirst threshold value, which is related to the first remaining capacity,is a threshold value set in advance as a lower-limit remaining capacityvalue that allows an output demand of the electric load greater than orequal to a predetermined value to be realized when power is suppliedonly from the first energy storage device to the electric load (a thirdaspect of the present disclosure).

Accordingly, during the execution of the control process based on thefirst control rule, if the first remaining capacity is reduced to aremaining capacity value that makes it difficult for the first energystorage device to supply a supplied power that allows an output demandof the electric load greater than or equal to a predetermined value tobe realized, the control process based on the second control rule isexecuted. This allows the control process based on the second controlprocess to start at an appropriate timing.

In the first to third aspects of the present disclosure, preferably, thecontrol device is configured to acquire a second remaining capacity thatis a remaining capacity of the second energy storage device, and isconfigured to execute the control process based on the second controlrule under a condition that the second remaining capacity is greaterthan or equal to a predetermined third threshold value and prohibitpower from being supplied from the second energy storage device to theelectric load when the second remaining capacity is smaller than thethird threshold value (a fourth aspect of the present disclosure).

This can prevent the remaining capacity of the second energy storagedevice (second remaining capacity) from being reduced below the thirdthreshold value, that is, from being brought into an over-discharged orsimilar state. Thus, the progress of deterioration of the second energystorage device can be prevented.

In the first to fourth aspects of the present disclosure, preferably,the control device is configured to acquire an output demand of theelectric load, and is configured to perform, in the control processbased on the first control rule, a process for controlling the powertransmission circuit unit to, when the output demand is smaller than apredetermined A-th threshold value, output from the first energy storagedevice a supplied power larger than a supplied power corresponding tothe output demand and charge the second energy storage device with aportion of the supplied power output from the first energy storagedevice (a fifth aspect of the present disclosure).

This allows the second energy storage device to be charged with aportion of the supplied power output from the first energy storagedevice, during the execution of the control process based on the firstcontrol rule, if the output demand is smaller than a predetermined A-ththreshold value. This can prevent a reduction in the remaining capacityof the second energy storage device (second remaining capacity) beforethe start of the control process based on the second control rule.

Thus, the period during which power can be supplied to the electric loadcan be extended as far as possible after the start of the controlprocess based on the second control mode.

In the fifth aspect of the present disclosure, preferably, the controldevice is configured to acquire a second remaining capacity that is aremaining capacity of the second energy storage device, and isconfigured to execute a process for controlling the power transmissioncircuit unit to charge the second energy storage device with the portionof the supplied power output from the first energy storage device, theprocess being included in the control process based on the first controlrule, under a condition that the second remaining capacity is less thanor equal to a predetermined fourth threshold value (a sixth aspect ofthe present disclosure).

The fourth threshold value is a threshold value larger than the thirdthreshold value in the fourth aspect of the present disclosure.

The sixth aspect of the present disclosure can prevent the second energystorage device from being charged with power supplied from the firstenergy storage device more than necessary during the execution of thecontrol process based on the first control rule. This can prevent theprogress of deterioration of the second energy storage device and canreduce the energy loss caused by the charging procedure.

In the first to sixth aspects of the present disclosure described above,the electric load may be, for example, an electric motor (a seventhaspect of the present disclosure).

In the seventh aspect of the present disclosure, preferably, the powertransmission circuit unit includes a voltage converter that converts anoutput voltage of at least one of the first energy storage device andthe second energy storage device to produce a voltage and outputs theproduced voltage, and an inverter that converts a direct-current powerinput from the first energy storage device, the second energy storagedevice, or the voltage converter into an alternating-current power andsupplies the alternating-current power to the electric motor (an eighthaspect of the present disclosure).

This allows appropriate control of power transmission among an electricmotor serving as the electric load, the first energy storage device, andthe second energy storage device.

Further, a transportation device according to another aspect of thepresent disclosure includes the power supply system according to thefirst to eighth aspect of the present disclosure (a ninth aspect of thepresent disclosure). The transportation device is implementable as atransportation device that achieves the advantages described above withreference to the first to eighth aspects of the present disclosure.

Further, a power transmission method according to still another aspectof the present disclosure is a power transmission method for powertransmission among an electric load, a first energy storage device, anda second energy storage device having a higher power density and a lowerenergy density than the first energy storage device in a power supplysystem, the power supply system including the first energy storagedevice and the second energy storage device and being configured tosupply power from at least one of the first energy storage device andthe second energy storage device to the electric load. The powertransmission method includes the steps of performing a control processbased on a first control rule to supply power from at least one of thefirst energy storage device and the second energy storage device to theelectric load when a first remaining capacity that is a remainingcapacity of the first energy storage device is larger than apredetermined first threshold value; performing a control process basedon a second control rule different from the first control rule to supplypower from one or both of the first energy storage device and the secondenergy storage device to the electric load, the one or both of the firstenergy storage device and the second energy storage device including atleast the first energy storage device, when the first remaining capacityis smaller than the first threshold value; and prohibiting power frombeing supplied from at least the first energy storage device to theelectric load when the first remaining capacity is smaller than apredetermined second threshold value smaller than the first thresholdvalue (a tenth aspect of the present disclosure).

This allows, as in the first aspect of the present disclosure, as muchenergy as possible to be supplied from two energy storage devices to theelectric load to enhance the efficiency of use of the energy. This makesit possible to extend the period during which the supplied powercorresponding to the output demand can be supplied to the electric load.

When the first remaining capacity is smaller than the second thresholdvalue, power is prohibited from being supplied from the first energystorage device to the electric load. This prevents the first energystorage device from being over-discharged. Thus, the progress ofdeterioration of the first energy storage device can be prevented.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

What is claimed is:
 1. A power supply system comprising: a first energystorage device; a second energy storage device having a higher powerdensity and a lower energy density than the first energy storage device;a power transmission circuit unit disposed in a power transmission pathamong an electric load, the first energy storage device, and the secondenergy storage device, the electric load being activated upon beingsupplied with power from at least one of the first energy storage deviceand the second energy storage device, the power transmission circuitunit being configured to be capable of controlling power transmissionamong the electric load, the first energy storage device, and the secondenergy storage device in accordance with a given control signal; and acontrol device configured to have a function of controlling the powertransmission circuit unit, wherein the control device is configured toacquire a first remaining capacity that is a remaining capacity of thefirst energy storage device, and is configured to control the powertransmission circuit unit to perform a control process based on a firstcontrol rule to supply power from at least one of the first energystorage device and the second energy storage device to the electric loadwhen the first remaining capacity is larger than a predetermined firstthreshold value, perform a control process based on a second controlrule different from the first control rule to supply power from one orboth of the first energy storage device and the second energy storagedevice to the electric load, the one or both of the first energy storagedevice and the second energy storage device including at least the firstenergy storage device, when the first remaining capacity is smaller thanthe first threshold value, and prohibit power from being supplied fromat least the first energy storage device to the electric load when thefirst remaining capacity is smaller than a predetermined secondthreshold value smaller than the first threshold value.
 2. The powersupply system according to claim 1, wherein the control device isconfigured to acquire an output demand of the electric load, and isconfigured to control the power transmission circuit unit to set, in thecontrol process based on the second control rule, a target value for asupplied power which is to be output from the first energy storagedevice in accordance with the first remaining capacity, when the targetvalue is smaller than a supplied power corresponding to the outputdemand, output a supplied power equal to the target value from the firstenergy storage device, and output from the second energy storage devicea supplied power equal to a difference obtained by subtracting thetarget value from the supplied power corresponding to the output demand,and when the target value is greater than or equal to the supplied powercorresponding to the output demand, output the supplied powercorresponding to the output demand from the first energy storage device.3. The power supply system according to claim 1, wherein the firstthreshold value, which is related to the first remaining capacity,comprises a threshold value set in advance as a lower-limit remainingcapacity value that allows an output demand of the electric load greaterthan or equal to a predetermined value to be realized when power issupplied only from the first energy storage device to the electric load.4. The power supply system according to claim 1, wherein the controldevice is configured to acquire a second remaining capacity that is aremaining capacity of the second energy storage device, and isconfigured to execute the control process based on the second controlrule under a condition that the second remaining capacity is greaterthan or equal to a predetermined third threshold value, and prohibitpower from being supplied from the second energy storage device to theelectric load when the second remaining capacity is smaller than thethird threshold value.
 5. The power supply system according to claim 1,wherein the control device is configured to acquire an output demand ofthe electric load, and is configured to perform, in the control processbased on the first control rule, a process for controlling the powertransmission circuit unit to, when the output demand is smaller than apredetermined A-th threshold value, output from the first energy storagedevice a supplied power larger than a supplied power corresponding tothe output demand, and charge the second energy storage device with aportion of the supplied power output from the first energy storagedevice.
 6. The power supply system according to claim 5, wherein thecontrol device is configured to acquire a second remaining capacity thatis a remaining capacity of the second energy storage device, and isconfigured to execute a process for controlling the power transmissioncircuit unit to charge the second energy storage device with the portionof the supplied power output from the first energy storage device, theprocess being included in the control process based on the first controlrule, under a condition that the second remaining capacity is less thanor equal to a predetermined fourth threshold value.
 7. The power supplysystem according to claim 1, wherein the electric load comprises anelectric motor.
 8. The power supply system according to claim 7, whereinthe power transmission circuit unit includes a voltage converter thatconverts an output voltage of at least one of the first energy storagedevice and the second energy storage device to produce a voltage andoutputs the produced voltage, and an inverter that converts adirect-current power input from the first energy storage device, thesecond energy storage device, or the voltage converter into analternating-current power and supplies the alternating-current power tothe electric motor.
 9. A transportation device comprising the powersupply system according to claim
 1. 10. A power transmission method forpower transmission among an electric load, a first energy storagedevice, and a second energy storage device having a higher power densityand a lower energy density than the first energy storage device in apower supply system, the power supply system including the first energystorage device and the second energy storage device and being configuredto supply power from at least one of the first energy storage device andthe second energy storage device to the electric load, the powertransmission method comprising the steps of: performing a controlprocess based on a first control rule to supply power from at least oneof the first energy storage device and the second energy storage deviceto the electric load when a first remaining capacity that is a remainingcapacity of the first energy storage device is larger than apredetermined first threshold value; performing a control process basedon a second control rule different from the first control rule to supplypower from one or both of the first energy storage device and the secondenergy storage device to the electric load, the one or both of the firstenergy storage device and the second energy storage device including atleast the first energy storage device, when the first remaining capacityis smaller than the first threshold value; and prohibiting power frombeing supplied from at least the first energy storage device to theelectric load when the first remaining capacity is smaller than apredetermined second threshold value smaller than the first thresholdvalue.
 11. A power supply system comprising: a first energy storage tosupply electric power to an electric load, the first energy storagehaving a first power density and a first energy density; a second energystorage to supply electric power to the electric load, the second energystorage having a second power density higher than a first power densityand a second energy density lower than the first energy density; a powertransmission circuit connected to the electric load, the first energystorage, and the second energy storage so as to control powertransmission among the electric load, the first energy storage, and thesecond energy storage; and circuitry configured to acquire a firstremaining capacity value indicating remaining capacity of the firstenergy storage; control the power transmission circuit to supply powerfrom at least one of the first energy storage and the second energystorage to the electric load when the first remaining capacity value islarger than a first threshold value; control the power transmissioncircuit to supply power from the first energy storage or both of thefirst energy storage and the second energy storage to the electric loadwhen the first remaining capacity value is smaller than the firstthreshold value; and control the power transmission circuit to stopsupplying power from the first energy storage to the electric load whenthe first remaining capacity value is smaller than a second thresholdvalue which is smaller than the first threshold value.
 12. The powersupply system according to claim 11, wherein the circuitry is configuredto acquire an output demand of the electric load, and is configured tocontrol the power transmission circuit to set a target value for asupplied power which is to be output from the first energy storage inaccordance with the first remaining capacity value, when the targetvalue is smaller than a supplied power corresponding to the outputdemand, output a supplied power equal to the target value from the firstenergy storage, and output from the second energy storage a suppliedpower equal to a difference obtained by subtracting the target valuefrom the supplied power corresponding to the output demand, and when thetarget value is greater than or equal to the supplied powercorresponding to the output demand, output the supplied powercorresponding to the output demand from the first energy storage. 13.The power supply system according to claim 11, wherein the firstthreshold value, which is related to the first remaining capacity value,comprises a threshold value set in advance as a lower-limit remainingcapacity value that allows an output demand of the electric load greaterthan or equal to a predetermined value to be realized when power issupplied only from the first energy storage to the electric load. 14.The power supply system according to claim 11, wherein the circuitry isconfigured to acquire a second remaining capacity value that is aremaining capacity of the second energy storage, and is configured tosupply power from the first energy storage or both of the first energystorage and the second energy storage to the electric load under acondition that the second remaining capacity value is greater than orequal to a predetermined third threshold value, and prohibit power frombeing supplied from the second energy storage to the electric load whenthe second remaining capacity value is smaller than the third thresholdvalue.
 15. The power supply system according to claim 11, wherein thecircuitry is configured to acquire an output demand of the electricload, and is configured to perform a process for controlling the powertransmission circuit to, when the output demand is smaller than apredetermined A-th threshold value, output from the first energy storagea supplied power larger than a supplied power corresponding to theoutput demand, and charge the second energy storage with a portion ofthe supplied power output from the first energy storage.
 16. The powersupply system according to claim 15, wherein the circuitry is configuredto acquire a second remaining capacity value that is a remainingcapacity of the second energy storage, and is configured to execute aprocess for controlling the power transmission circuit to charge thesecond energy storage with the portion of the supplied power output fromthe first energy storage, under a condition that the second remainingcapacity value is less than or equal to a predetermined fourth thresholdvalue.
 17. The power supply system according to claim 11, wherein theelectric load comprises an electric motor.
 18. The power supply systemaccording to claim 17, wherein the power transmission circuit includes avoltage converter that converts an output voltage of at least one of thefirst energy storage and the second energy storage to produce a voltageand outputs the produced voltage, and an inverter that converts adirect-current power input from the first energy storage, the secondenergy storage, or the voltage converter into an alternating-currentpower and supplies the alternating-current power to the electric motor.19. A transportation device comprising the power supply system accordingto claim
 11. 20. A power transmission method comprising: acquiring afirst remaining capacity value indicating remaining capacity of a firstenergy storage; supplying power from at least one of the first energystorage and a second energy storage to an electric load when the firstremaining capacity value is larger than a first threshold value;supplying power from the first energy storage or both of the firstenergy storage and the second energy storage to the electric load whenthe first remaining capacity value is smaller than the first thresholdvalue; and stopping supplying power from the first energy storage to theelectric load when the first remaining capacity value is smaller than asecond threshold value which is smaller than the first threshold value.